Apparatus and method for transmitting and receiving fast feedback information in broadband wireless communication system

ABSTRACT

An apparatus and method for operating a fast feedback channel in a broadband wireless communication system are provided. The method includes generating and transmitting a feedback signal through a fast feedback channel of a first mode, determining to switch a mode of the fast feedback channel from the first mode to a second mode, transmitting a signal for requesting the mode switching of the fast feedback channel through the fast feedback channel, and generating and transmitting a feedback signal through a fast feedback channel of the second mode.

PRIORITY

This application claims the benefit under 35 U.S.C. §119(a) of a Koreanpatent application filed in the Korean Intellectual Property Office onAug. 29, 2008 and assigned Serial No. 10-2008-0084922 and a Koreanpatent application filed in the Korean Intellectual Property Office onJul. 6, 2009 and assigned Serial No. 10-2009-0061261, the entiredisclosures of both of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a broadband wireless communicationsystem. More particularly, the present invention relates to an apparatusand method for transmitting and receiving information through a fastfeedback channel in a broadband wireless communication system.

2. Description of the Related Art

In the next generation communication system, also known as the 4^(th)Generation (4G) communication system, research is being activelyconducted to provide a Quality of Service (QoS) with a data transferspeed of about 100 Mbps. An example of such a communication system is anInstitute of Electrical and Electronics Engineers (IEEE) 802.16 system.The IEEE 802.16 system employs an Orthogonal Frequency DivisionMultiplexing (OFDM)/Orthogonal Frequency Division Multiple Access(OFDMA) scheme so that a broadband network can be supported in aphysical channel.

In a broadband wireless communication system such as the IEEE 802.16system, Mobile Stations (MSs) located within a cell periodicallytransmit feedback information to a Base Station (BS). The feedbackinformation can represent a forward channel state through additionalphysical channels allocated along frequency and time axes. Examples ofthe feedback information include Channel Quality Indication (CQI)information such as a Carrier to Interference and Noise Ratio (CINR) anda Modulation and Coding Scheme (MCS), sub-band information having anexcellent channel property, and a Precoding Matrix Index (PMI) ofMultiple Input Multiple Output (MIMO). The feedback information may onlybe a small amount of information but is significantly important in theoperation of the communication system and thus requires high reliabilityto support the entire cell area including a cell edge. Alternatively,the feedback information may be information having a large amount ofinformation to support a MIMO mode operated in a high Signal to NoiseRatio (SNR) environment.

A fast feedback channel supporting the entire cell area has to bedesigned to have a robust structure so that a region of a low SNR canalso be supported with a small amount of information. Therefore, in acommunication system such as the IEEE 802.16 system, a noncoherentmodulation/demodulation scheme is used for the fast feedback channel.That is, a transmitting end assigns a code sequence, corresponding toinformation to be transmitted, to an allocated resource and thentransmits the resultant code sequence, and a receiving end searches fora code sequence corresponding to a maximum value among correlationvalues between each of all code sequences and a received signal.

With the recent development of multimedia technologies and the increasein demands thereof, a high data rate is necessary and thus a recentlydeveloped communication system actively adopts an improved techniquesuch as MIMO for the support of the high data rate. Unlike in aconventional communication system which uses a level of CQI informationas feedback information, a technique such as Closed-Loop (CL)-MIMOrequires a relatively large amount of feedback information, e.g., a PMI,a rank, etc. However, an amount of feedback information transmittablethrough the fast feedback channel is limited by a length of the codesequence. If to-be-transmitted feedback information has a length greaterthan or equal to the code sequence, a plurality of fast feedbackchannels has to be allocated to a single MS.

As described above, since a large amount of feedback information isrequired, a currently available method for operating the fast feedbackchannel is not suitable to effectively transmit a required amount ofinformation. Therefore, there is a need for a method for effectivelyoperating a fast feedback channel with a limited amount of resources ina broadband wireless communication system in which a variety of feedbackinformation exists.

SUMMARY OF THE INVENTION

An aspect of the present invention is to address at least theabove-mentioned problems and/or disadvantages and to provide at leastthe advantages described below. Accordingly, an aspect of the presentinvention is to provide an apparatus and method for effectivelyoperating a fast feedback channel with a limited amount of resources ina broadband wireless communication system.

Another aspect of the present invention is to provide an apparatus andmethod for selectively applying a noncoherent modulation/demodulationscheme and a coherent modulation/demodulation scheme to a fast feedbackchannel in a broadband wireless communication system.

Yet another aspect of the present invention is to provide an apparatusand method for requesting the mode switching of a fast feedback channelin a broadband wireless communication system.

Still another aspect of the present invention is to provide an apparatusand method for determining a mode of a fast feedback channel accordingto a type of feedback information in a broadband wireless communicationsystem.

In accordance with an aspect of the present invention, a method foroperating a Mobile Station (MS) in a broadband wireless communicationsystem using a fast feedback channel supporting at least two modes isprovided. The method includes generating and transmitting a feedbacksignal through a fast feedback channel of a first mode, determining toswitch a mode of the fast feedback channel from the first mode to asecond mode, transmitting a signal for requesting the mode switching ofthe fast feedback channel through the fast feedback channel, andgenerating and transmitting a feedback signal through a fast feedbackchannel of the second mode.

In accordance with another aspect of the present invention, a method foroperating a Base Station (BS) in a broadband wireless communicationsystem using a fast feedback channel supporting at least two modes isprovided. The method includes detecting feedback information from afeedback signal received through the fast feedback channel according toa first mode, receiving a signal for requesting the mode switching fromthe first mode to a second mode through the fast feedback channel, anddetecting the feedback information from the feedback signal receivedthrough the fast feedback channel according to the second mode.

In accordance with yet another aspect of the present invention, a MobileStation (MS) apparatus in a broadband wireless communication systemusing a fast feedback channel supporting at least two modes is provided.The apparatus includes a first configuration unit for generating afeedback signal to be transmitted through a fast feedback channel of afirst mode, a second configuration unit for generating a feedback signalto be transmitted through a fast feedback channel of a second mode, atransmitter for transmitting the feedback signal, and a determinationunit for controlling feedback signal generation operations of the firstand second configuration units according to a mode of the fast feedbackchannel, and if it is determined that the fast feedback channel changesits mode from the first mode to the second mode, for providing controlsuch that a signal for mode switching of the fast feedback channel istransmitted through the fast feedback channel and for determiningswitching to the second mode.

In accordance with still another aspect of the present invention, a BaseStation (BS) apparatus in a broadband wireless communication systemusing a fast feedback channel supporting at least two modes is provided.The apparatus includes a first detector for detecting feedbackinformation from a feedback signal received through the fast feedbackchannel according to a first mode, a second detector for detectingfeedback information from a feedback signal received through the fastfeedback channel according to a second mode, and a manager forcontrolling operations of the first and second detectors according to amode of the feedback channel, and if a signal for requesting the modeswitching from the first mode to the second mode is detected through thefast feedback channel, for stopping the detection operation of the firstdetector and for controlling the second detector to detect feedbackinformation according to the second mode.

Other aspects, advantages, and salient features of the invention willbecome apparent to those skilled in the art from the following detaileddescription, which, taken in conjunction with the annexed drawings,discloses exemplary embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features, and advantages of certainexemplary embodiments of the present invention will be more apparentfrom the following description taken in conjunction with theaccompanying drawings, in which:

FIG. 1 illustrates a structure of a fast feedback channel in a broadbandwireless communication system according to an exemplary embodiment ofthe present invention;

FIG. 2 illustrates a structure of a Basic Feedback Channel (BFCH) in abroadband wireless communication system according to an exemplaryembodiment of the present invention;

FIG. 3 illustrates a structure of an Enhanced Feedback Channel (EFCH) ina broadband wireless communication system according to an exemplaryembodiment of the present invention;

FIG. 4 illustrates a structure of a bit-stream transmitted through anEFCH in a broadband wireless communication system according to anexemplary embodiment of the present invention;

FIG. 5 illustrates a process of switching from a BFCH mode to an EFCHmode in a broadband wireless communication system according to anexemplary embodiment of the present invention;

FIG. 6 illustrates a process of switching from a BFCH mode to an EFCHmode under the control of a Base Station (BS) in a broadband wirelesscommunication system according to an exemplary embodiment of the presentinvention;

FIG. 7 illustrates a process of switching from an EFCH mode to a BFCHmode by using a code sequence of the BFCH mode in a broadband wirelesscommunication system according to an exemplary embodiment of the presentinvention;

FIG. 8 illustrates a process of switching from an EFCH mode to a BFCHmode by using an indicator of the EFCH mode in a broadband wirelesscommunication system according to an exemplary embodiment of the presentinvention;

FIG. 9 illustrates a process of temporarily switching from an EFCH modeto a BFCH mode by using an indicator of the EFCH mode in a broadbandwireless communication system according to an exemplary embodiment ofthe present invention;

FIG. 10 illustrates a process of temporarily switching from an EFCH modeto a BFCH mode by using an indicator of the EFCH mode and then switchingto the BFCH mode by using a code sequence of the BFCH mode in abroadband wireless communication system according to an exemplaryembodiment of the present invention;

FIG. 11 illustrates a process of periodically switching to a BFCH modewhile temporarily switching from an EFCH mode to the BFCH mode by usingan indicator of the EFCH mode in a broadband wireless communicationsystem according to an exemplary embodiment of the present invention;

FIG. 12 is a flowchart illustrating an operation of a Mobile Station(MS) for switching a feedback mode without control of a BS in abroadband wireless communication system according to an exemplaryembodiment of the present invention;

FIG. 13 is a flowchart illustrating an operation of a BS which does notcontrol switching of a feedback mode in a broadband wirelesscommunication system according to an exemplary embodiment of the presentinvention;

FIG. 14 is a flowchart illustrating an operation of an MS for switchingfrom a BFCH mode to an EFCH mode under the control of a BS in abroadband wireless communication system according to an exemplaryembodiment of the present invention;

FIG. 15 is a flowchart illustrating an operation of a BS for controllingswitching from a BFCH mode to an EFCH mode in a broadband wirelesscommunication system according to an exemplary embodiment of the presentinvention;

FIG. 16 is a flowchart illustrating an operation of an MS fortemporarily switching from an EFCH mode to a BFCH mode in a broadbandwireless communication system according to an exemplary embodiment ofthe present invention;

FIG. 17 is a flowchart illustrating an operation of a BS correspondingto an MS for temporarily switching from an EFCH mode to a BFCH mode in abroadband wireless communication system according to an exemplaryembodiment of the present invention;

FIG. 18 is a flowchart illustrating an operation of an MS for switchingto a temporary BFCH mode and for requesting switching to a BFCH modefrom the temporary BFCH mode in a broadband wireless communicationsystem according to an exemplary embodiment of the present invention;

FIG. 19 is a flowchart illustrating an operation of a BS correspondingto an MS for switching to a temporary BFCH mode and for requestingswitching to a BFCH mode from the temporary BFCH mode in a broadbandwireless communication system according to an exemplary embodiment ofthe present invention;

FIG. 20 is a flowchart illustrating an operation of an MS for requestingswitching to a temporary BFCH mode while periodically switching to aBFCH mode in a broadband wireless communication system according to anexemplary embodiment of the present invention;

FIG. 21 is a flowchart illustrating an operation of a BS correspondingto an MS for requesting switching to a temporary BFCH mode whileperiodically switching to a BFCH mode in a broadband wirelesscommunication system according to an exemplary embodiment of the presentinvention;

FIG. 22A to FIG. 22C are block diagrams illustrating a structure of anMS in a broadband wireless communication system according to anexemplary embodiment of the present invention; and

FIG. 23A to FIG. 23C are block diagrams illustrating a structure of a BSin a broadband wireless communication system according to an exemplaryembodiment of the present invention.

Throughout the drawings, it should be noted that like reference numbersare used to depict the same or similar elements, features andstructures.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

The following description with reference to the accompanying drawings isprovided to assist in a comprehensive understanding of exemplaryembodiments of the invention as defined by the claims and theirequivalents. It includes various specific details to assist in thatunderstanding but these are to be regarded as merely exemplary.Accordingly, those of ordinary skill in the art will recognize thatvarious changes and modifications of the embodiments described hereincan be made without departing from the scope and spirit of theinvention. Also, descriptions of well-known functions and constructionsare omitted for clarity and conciseness.

The terms and words used in the following description and claims are notlimited to the bibliographical meanings, but, are merely used by theinventor to enable a clear and consistent understanding of theinvention. Accordingly, it should be apparent to those skilled in theart that the following description of exemplary embodiments of thepresent invention are provided for illustration purpose only and not forthe purpose of limiting the invention as defined by the appended claimsand their equivalents.

It is to be understood that the singular forms “a,” “an,” and “the”include plural referents unless the context clearly dictates otherwise.Thus, for example, reference to “a component surface” includes referenceto one or more of such surfaces.

By the term “substantially” it is meant that the recited characteristic,parameter, or value need not be achieved exactly, but that deviations orvariations, including for example, tolerances, measurement error,measurement accuracy limitations and other factors known to those ofskill in the art, may occur in amounts that do not preclude the effectthe characteristic was intended to provide.

Hereinafter, a technique for effectively operating a fast feedbackchannel with a limited amount of resources in a broadband wirelesscommunication system will be described. Although an Orthogonal FrequencyDivision Multiplexing (OFDM)/Orthogonal Frequency Division MultipleAccess (OFDMA)-based wireless communication system is describedhereinafter for example, the present invention can also equally apply toother types of wireless communication system.

FIG. 1 illustrates a structure of a fast feedback channel in a broadbandwireless communication system according to an exemplary embodiment ofthe present invention.

Referring to FIG. 1, a fast feedback channel having a structure of FIG.1 is assumed in an exemplary embodiment of the present invention. Thatis, the fast feedback channel consists of three sub-carrier bundles 111,113, and 115, and each sub-carrier bundle includes two sub-carriers and6 OFDM symbols. That is, one sub-carrier bundle includes 12 modulationsymbols. However, an exemplary embodiment of the present invention mayalso equally apply to wireless communication systems using other typesof fast feedback channels.

In order to effectively operate a fast feedback channel with a limitedamount of resources, a broadband wireless communication system accordingto an exemplary embodiment of the present invention selectively uses twotypes of fast feedback channels as illustrated in FIG. 2 and FIG. 3. Forconvenience of explanation, the fast feedback channel of FIG. 2 isreferred to as a Basic Feedback Channel (BFCH), and the fast feedbackchannel of FIG. 3 is referred to as an Enhanced Feedback Channel (EFCH).According to an exemplary embodiment of the present invention, the BFCHand the EFCH use a tile consisting of 2 contiguous sub-carriers and 6OFDM symbols as a basic structure and the basic structure of the tilecan be modified in any frequency and time according to an exemplaryembodiment of the present invention.

FIG. 2 illustrates a structure of a Basic Feedback Channel (BFCH) in abroadband wireless communication system according to an exemplaryembodiment of the present invention.

Referring to FIG. 2, the BFCH is a fast feedback channel which uses anoncoherent modulation/demodulation scheme. A code sequence Ck with alength of 12 is transmitted through the BFCH. That is, in the BFCH,elements Ck,0 to Ck,11 of the code sequence Ck are assigned torespective tones within a tile, and may be redundantly assigned to aplurality of tiles to obtain a diversity gain.

FIG. 3 illustrates a structure of an Enhanced Feedback Channel (EFCH) ina broadband wireless communication system according to an exemplaryembodiment of the present invention.

Referring to FIG. 3, the EFCH is a fast feedback channel which uses acoherent modulation/demodulation scheme, and includes a pilot symbol. 4pilot symbols and 8 feedback information symbols are transmitted throughthe EFCH. That is, in the EFCH, pilot symbols are allocated to sometones for coherent demodulation. Channel-coded and modulated feedbackinformation symbols are allocated to tones other than the tones to whichthe pilot symbols are allocated. Herein, the number of pilot symbols andthe positions thereof may change variously according to an exemplaryimplementation.

If the fast feedback channel consists of 3 tiles as illustrated in FIG.1, an amount of information transmissible through the EFCH is 24 bitswhen using channel coding with a ½ coding rate and is 16 bits when usingchannel coding with a ⅓ coding rate. The amount of informationtransmissible through the EFCH is greater than an amount of informationtransmissible through the BFCH. Further, the amount of informationtransmissible through the EFCH can be regulated by differently settingthe number of pilot symbols and the coding rate.

In the broadband wireless communication system according to an exemplaryembodiment of the present invention, the fast feedback channel is theBFCH by default, and switches to the EFCH when an amount of feedbackinformation increases. Of course, the fast feedback channel may alsoswitch from the EFCH to the BFCH when the amount of feedback informationdecreases.

The BFCH used in the broadband wireless communication system accordingto an exemplary embodiment of the present invention is a basic feedbackchannel that may support an entire cell area used for the purpose ofChannel Quality Indicator (CQI) information transmission. That is, theBFCH is basically allocated to a Mobile Station (MS) when communicationis made between a Base Station (BS) and the MS, and the MS persistentlyfeeds back CQI information according to a period assigned by the BS. Forexample, code sequences for the BFCH have an information amount of 6bits as shown in Table 1 below, and use 5 bits to represent the CQIinformation.

TABLE 1 Fast feedback payload Code sequence Notes 0b000000 C0 IndicateCQI 0b000001 C1 (5 LSB bits) 0b000010 C2 0b000011 C3 0b000100 C40b000101 C5 0b000110 C6 . . . . . . 0b011110 C30 0b011111 C31 0b100000C32 Extra usages . . . . . . 0b111101 C61 0b111110 C62 E1 (switch toEFCH from BFCH) 0b111111 C63 E2 (switch to BFCH from EFCH)

Referring to Table 1 above, code sequences C₀ to C₃₁ are used toindicate CQI, and code sequences C₃₂ to C₆₂ are used for extra usages. Acode sequence C₆₂ may be used for a request of switching from a BFCHmode to an EFCH mode. A code sequence C₆₃ may be used for a request ofswitching from the EFCH mode to the BFCH mode. Examples of the extrausages include a bandwidth request, a preferred Multiple Input MultipleOutput (MIMO) mode, frequency partition selection, etc.

Mode switching of the feedback channel is determined according tochanges in a type of feedback information. The type of feedbackinformation is determined according to an operation mode of the MS.Consequently, a mode of the feedback channel is determined by theoperation mode of the MS. Although code sequences dedicatedly allocatedfor mode switching, e.g., an E1 code and an E2 code, can be used torequest mode switching as described above, according to anotherexemplary embodiment of the present invention, code sequences forreporting the preferred MIMO mode among the code sequences allocated forthe extra usages can be used as code sequences for requesting the modeswitching. In this case, possible modes of the feedback channel may bethree or more types of modes including a plurality of EFCH modes andBFCH modes rather than two types of modes, i.e., the EFCH mode and theBFCH mode.

When using the fast feedback channel as illustrated in FIG. 1, thenumber of tones constituting a code sequence is 12. That is, a length ofthe code sequence is 12. When considering the code sequence with alength of 12, the 64 code sequences of Table 1 above are not generatedif an orthogonal code sequence set is constructed. Therefore, totransmit and receive the 64 code sequences through the fast feedbackchannel of FIG. 1, an exemplary embodiment of the present invention mayuse a quasi-orthogonal code sequence set. In other words, the broadbandwireless communication system uses 64 quasi-orthogonal code sequences bycombining different phase vectors with a code sequence consisting of thesame combination while using code sequences constructed of all possiblecombinations of different orthogonal sub-code sequences. For example,when 4 orthogonal sub-code sequences exist, 16 combinations are possiblein total, and 64 quasi-orthogonal code sequences are generated byapplying 4 phase vectors to each of the 16 combinations. Table 2 belowshows an example of a quasi-orthogonal code sequence set generatedaccording to the aforementioned method.

TABLE 2 index of phase difference sub-signal stream vector signal streamcodeword (l, m, n) (BPSK) (BPSK) 0b000000 (0, 0, 0) (1, 1, 1)111111111111 0b000001 (0, 0, 0) (1, −1, 1) 111100001111 0b000010 (0, 0,0) (1, 1, −1) 111111110000 0b000011 (0, 0, 0) (1, −1, −1) 1111000000000b000100 (0, 1, 2) (1, 1, 1) 111111001001 0b000101 (0, 1, 2) (1, −1, 1)111100111001 0b000110 (0, 1, 2) (1, 1, −1) 111111000110 0b000111 (0, 1,2) (1, −1, −1) 111100110110 0b001000 (0, 2, 3) (1, 1, 1) 1111001110100b001001 (0, 2, 3) (1, −1, 1) 111101101010 0b001010 (0, 2, 3) (1, 1, −1)111110010101 0b001011 (0, 2, 3) (1, −1, −1) 111101100101 0b001100 (0,3, 1) (1, 1, 1) 111110101100 0b001101 (0, 3, 1) (1, −1, 1) 1111010111000b001110 (0, 3, 1) (1, 1, −1) 111110100011 0b001111 (0, 3, 1) (1, −1,−1) 111101010011 0b010000 (1, 2, 0) (1, 1, 1) 110010011111 0b010001 (1,2, 0) (1, −1, 1) 110001101111 0b010010 (1, 2, 0) (1, 1, −1) 1100100100000b010011 (1, 2, 0) (1, −1, −1) 110001100000 0b010100 (2, 3, 0) (1, 1, 1)100110101111 0b010101 (2, 3, 0) (1, −1, 1) 100101011111 0b010110 (2, 3,0) (1, 1, −1) 100110100000 0b010111 (2, 3, 0) (1, −1, −1) 1001010100000b011000 (3, 1, 0) (1, 1, 1) 101011001111 0b011001 (3, 1, 0) (1, −1, 1)101000111111 0b011010 (3, 1, 0) (1, 1, −1) 101011000000 0b011011 (3, 1,0) (1, −1, −1) 101000110000 0b011100 (2, 0, 1) (1, 1, 1) 1001111111000b011101 (2, 0, 1) (1, −1, 1) 100100001100 0b011110 (2, 0, 1) (1, 1, −1)100111110011 0b011111 (2, 0, 1) (1, −1, −1) 100100000011 0b100000 (3, 0,2) (1, 1, 1) 101011111001 0b100001 (3, 0, 2) (1, −1, 1) 1010000010010b100010 (3, 0, 2) (1, 1, −1) 101011110110 0b100011 (3, 0, 2) (1, −1,−1) 101000000110 0b100100 (1, 0, 3) (1, 1, 1) 110011111010 0b100101 (1,0, 3) (1, −1, 1) 110000001010 0b100110 (1, 0, 3) (1, 1, −1) 1100111101010b100111 (1, 0, 3) (1, −1, −1) 110000000101 0b101000 (1, 3, 2) (1, 1, 1)110010101001 0b101001 (1, 3, 2) (1, −1, 1) 110001011001 0b101010 (1, 3,2) (1, 1, −1) 110010100110 0b101011 (1, 3, 2) (1, −1, −1) 1100010101100b101100 (2, 1, 3) (1, 1, 1) 100111001010 0b101101 (2, 1, 3) (1, −1, 1)100100111010 0b101110 (2, 1, 3) (1, 1, −1) 100111000101 0b101111 (2, 1,3) (1, −1, −1) 100100110101 0b110000 (3, 2, 1) (1, 1, 1) 1010100111000b110001 (3, 2, 1) (1, −1, 1) 101001101100 0b110010 (3, 2, 1) (1, 1, −1)101010010011 0b110011 (3, 2, 1) (1, −1, −1) 101001100011 0b110100 (1,1, 1) (1, 1, 1) 110011001100 0b110101 (1, 1, 1) (1, −1, 1) 1100001111000b110110 (1, 1, 1) (1, 1, −1) 110011000011 0b110111 (1, 1, 1) (1, −1,−1) 110000110011 0b111000 (2, 2, 2) (1, 1, 1) 100110011001 0b111001 (2,2, 2) (1, −1, 1) 100101101001 0b111010 (2, 2, 2) (1, 1, −1) 1001100101100b111011 (2, 2, 2) (1, −1, −1) 100101100110 0b111100 (3, 3, 3) (1, 1, 1)101010101010 0b111101 (3, 3, 3) (1, −1, 1) 101001011010 0b111110 (3, 3,3) (1, 1, −1) 101010100101 0b111111 (3, 3, 3) (1, −1, −1) 101001010101

When the MS using the BFCH intends to transmit feedback information tosupport a MIMO mode, the BFCH is inappropriate due to a limited amountof information. Thus, the MS determines switching to the EFCH, transmitsa predefined E1 code to the BS through the BFCH to report thedetermination result. In this case, since the BS is in a state ofreceiving feedback information of the MS through the BFCH, the BSdetects the E1 code by performing code sequence detection usingcorrelation values. Accordingly, the BS recognizes that the MS hasrequested switching to the EFCH mode, and switches the mode of the fastfeedback channel of the MS to the EFCH mode in a next frame. Since theBFCH and the EFCH have the same resource structure, the switching to theEFCH mode does not require an additional resource allocation process. Inanother case, if the BS instructs the switching to the EFCH mode, thesystem defines a feedback channel type switch field in a map message,and the BS instructs the switching to the EFCH mode by using thefeedback channel type switch field. In still another case, if a requestand permission operation is required, mode switching is requested by theMS, and in response thereto, the BS permits the mode switching by usingthe map message.

When the MS moves to a cell edge and thus an amount of feedbackinformation decreases, the MIMO mode cannot be supported and thus anamount of feedback information decreases. Then, the MS determines toreturn to the BFCH mode and reports the determination result to the BS.In this case, two methods are proposed according to exemplaryembodiments of the present invention. First, a field for reportingswitching to the BFCH mode is defined among feedback information for theEFCH, and a bit of the field is set to ‘1’ if the switching to the BFCHmode is requested, and the bit of the field is set to ‘0’ if the EFCHmode is maintained. An example of constructing a feedback bit-streamtransmitted through the EFCH according to the first method is shown inFIG. 4. That is, as shown in FIG. 4, the feedback bit-stream includes aninformation bit-stream 410 and a mode switch indication bit 420. Second,an E2 code for a request of switching to the BFCH mode is defined amongcode sequences for the BFCH, and returning to the BFCH is requested whenthe MS transmits the E2 code. In the second method, the BS and the MSboth use a fast feedback channel of the EFCH mode, and the BS has toperform both coherent demodulation conforming to the EFCH mode andnoncoherent demodulation conforming to the BFCH mode. In another case,if the switching to the BFCH mode is instructed by the BS, the systemdefines a feedback channel type switch field in a map message, and theBS instructs the switching to the BFCH mode by using the feedbackchannel type switch field. In still another case, if a request andpermission operation is required, mode switching is requested by the MS,and in response thereto, the BS permits the mode switching by using themap message.

The BS recognizes the request of the MS for switching to the BFCH modeby using one of the two methods described above, and determines theswitching to the BFCH mode in a next frame. According to an exemplaryembodiment of the present invention, both or either one of the twomethods may be used by selection of each MS. When the second method isused, the BS first attempts to detect a feedback bit-stream receivedthrough a fast feedback channel of the EFCH mode, and if an error occursin the detection process, the BS attempts to detect the E2 code.

Hereinafter, an exemplary embodiment of switching between a BFCH modeand an EFCH mode according to the aforementioned mode switching methodwill be described.

FIG. 5 illustrates a process of switching from a BFCH mode to an EFCHmode in a broadband wireless communication system according to anexemplary embodiment of the present invention.

Referring to FIG. 5, an MS 502 transmits feedback information to a BS504 through a feedback channel of the BFCH mode. In this case, thefeedback information is periodically transmitted. While operating in theBFCH mode, the MS 502 determines switching to the EFCH mode andtransmits a mode switch request code sequence 510 through the feedbackchannel of the BFCH mode. For example, the mode switch request codesequence 510 is either an E1 code dedicatedly allocated for switchingfrom the BFCH mode to the EFCH mode or a code sequence indicating apreferred MIMO mode corresponding to a target EFCH mode to be switched.Thereafter, the MS 502 switches to the EFCH mode, and periodicallytransmits feedback information through a feedback channel of the EFCHmode. Herein, a feedback period of the BFCH mode and a feedback periodof the EFCH mode may be substantially identical to or different fromeach other.

FIG. 6 illustrates a process of switching from a BFCH mode to an EFCHmode under the control of a BS in a broadband wireless communicationsystem according to an exemplary embodiment of the present invention.

Referring to FIG. 6, an MS 602 transmits feedback information to a BS604 through a feedback channel of the BFCH mode. In this case, thefeedback information is periodically transmitted. While operating in theBFCH mode, the MS 602 determines switching to the EFCH mode andtransmits a mode switch request code sequence 610 through the feedbackchannel of the BFCH mode. For example, the mode switch request codesequence 610 is either an E1 code dedicatedly allocated for switchingfrom the BFCH mode to the EFCH mode or a code sequence indicating apreferred MIMO mode corresponding to a target EFCH mode to be switched.Unlike in the exemplary embodiment of FIG. 5, a permission of the BS 602is required in the exemplary embodiment of FIG. 6, rather than modeswitching is achieved only with the mode switch request code sequence610. Therefore, the MS 602 remains in the BFCH mode after transmittingthe mode switch request code sequence 610. In this case, the BS 604determines whether a mode switch request of the MS is permitted, and ifit is permitted, transmits feedback channel allocation information 620.The feedback channel allocation information 620 includes informationindicating a feedback channel location, a feedback period, a feedbackmode, etc. That is, when the feedback channel allocation information 620is used, the feedback channel may be relocated. Upon receiving thefeedback channel allocation information 620, the MS 602 switches to theEFCH mode, and periodically transmits feedback information through afeedback channel of the EFCH mode. Herein, a feedback period of the BFCHmode and a feedback period of the EFCH mode may be substantiallyidentical to or different from each other.

FIG. 7 illustrates a process of switching from an EFCH mode to a BFCHmode by using a code sequence of the BFCH mode in a broadband wirelesscommunication system according to an exemplary embodiment of the presentinvention.

Referring to FIG. 7, an MS 702 transmits feedback information to a BS704 through a feedback channel of the EFCH mode. In this case, thefeedback information is periodically transmitted. While operating in theEFCH mode, the MS 702 determines switching to the BFCH mode andtransmits a mode switch request code sequence 710 through a feedbackchannel of the BFCH mode. For example, the mode switch request codesequence 710 is either an E2 code dedicatedly allocated for switchingfrom the EFCH mode to the BFCH mode or a code sequence indicating apreferred MIMO mode using the BFCH mode. Thereafter, the MS 702periodically transmits feedback information through the feedback channelof the BFCH mode. Herein, a feedback period of the EFCH mode and afeedback period of the BFCH mode may be substantially identical to ordifferent from each other.

FIG. 8 illustrates a process of switching from an EFCH mode to a BFCHmode by using an indicator of the EFCH mode in a broadband wirelesscommunication system according to an exemplary embodiment of the presentinvention.

Referring to FIG. 8, an MS 802 transmits feedback information to a BS804 through a feedback channel of the EFCH mode. In this case, thefeedback information is periodically transmitted. While operating in theEFCH mode, the MS 802 determines switching to the BFCH mode andtransmits feedback information including a mode switch request 810through the feedback channel of the EFCH mode. For example, the modeswitching request implies an activated mode switch indication bit ofFIG. 4 above. That is, an indicator indicating the mode switch requestis included in the feedback information transmitted according to theEFCH mode, and the indicator is set to an activated value if modeswitching is requested, and is set to an inactivated value if modeswitching is not requested. However, the feedback informationtransmitted according to the EFCH mode may have various formats, and inthis case, feedback information of all formats may include theindicator, or only feedback information of some formats may include theindicator. Thereafter, the MS 802 switches to the BFCH mode, andperiodically transmits feedback information through a feedback channelof the BFCH mode. Herein, a feedback period of the EFCH mode and afeedback period of the BFCH mode may be substantially identical to ordifferent from each other.

FIG. 9 illustrates a process of temporarily switching from an EFCH modeto a BFCH mode by using an indicator of the EFCH mode in a broadbandwireless communication system according to an exemplary embodiment ofthe present invention.

Referring to FIG. 9, an MS 902 transmits feedback information to a BS904 through a feedback channel of the EFCH mode. In this case, thefeedback information is periodically transmitted. While operating in theEFCH mode, the MS 902 determines switching to the BFCH mode andtransmits feedback information including a mode switch request 910through the feedback channel of the EFCH mode. For example, the modeswitching request implies an activated mode switch indication bit ofFIG. 4 above. That is, an indicator indicating the mode switch requestis included in the feedback information transmitted according to theEFCH mode, and the indicator is set to an activated value if modeswitching is requested, and is set to an inactivated value if modeswitching is not requested. However, the feedback informationtransmitted according to the EFCH mode may have various formats, and inthis case, feedback information of all formats may include theindicator, or only feedback information of some formats may include theindicator. Unlike in the embodiment of FIG. 8, the switching to the BFCHmode is temporarily achieved in the present embodiment, rather than modeswitching is achieved completely at the mode switching request.Thereafter, the MS 902 switches to the BFCH mode, periodically transmitsfeedback information through a feedback channel of the BFCH mode duringa duration K 920, and returns to the EFCH mode. Herein, a feedbackperiod of the EFCH mode and a feedback period of the BFCH mode may besubstantially identical to or different from each other.

FIG. 10 illustrates a process of temporarily switching from an EFCH modeto a BFCH mode by using an indicator of the EFCH mode and then switchingto the BFCH mode by using a code sequence of the BFCH mode in abroadband wireless communication system according to an exemplaryembodiment of the present invention.

Referring to FIG. 10, an MS 1002 transmits feedback information to a BS1004 through a feedback channel of the EFCH mode. In this case, thefeedback information is periodically transmitted. While operating in theEFCH mode, the MS 1002 determines switching to the BFCH mode andtransmits feedback information including a mode switch request 1010through the feedback channel of the EFCH mode. For example, the modeswitching request implies an activated mode switch indication bit ofFIG. 4 above. That is, an indicator indicating the mode switch requestis included in the feedback information transmitted according to theEFCH mode, and the indicator is set to an activated value if modeswitching is requested, and is set to an inactivated value if modeswitching is not requested. However, the feedback informationtransmitted according to the EFCH mode may have various formats, and inthis case, feedback information of all formats may include theindicator, or only feedback information of some formats may include theindicator. Switching to the BFCH mode is temporarily achieved in thepresent embodiment, rather than mode switching is achieved completely atthe mode switching request. Thereafter, the MS 1002 switches to the BFCHmode, periodically transmits feedback information through a feedbackchannel of the BFCH mode during a duration K 1020, and returns to theEFCH mode. In this case, the MS 1002 transmits a mode switch requestcode sequence 1030 through the feedback channel of the BFCH mode duringthe duration K 1020. For example, the mode switch request code sequence1030 is either an E2 code dedicatedly allocated for switching from theEFCH mode to the BFCH mode or a code sequence indicating a preferredMIMO mode using the BFCH mode. Although it is shown in FIG. 10 that themode switch request code sequence 1030 is transmitted by feedback of thelast BFCH mode, the mode switch request code sequence 1030 may also betransmitted by feedback of the first BFCH mode or feedback of anotherBFCH mode. A permission of the BS 1004 is required in an exemplaryembodiment of the present embodiment, rather than mode switching isachieved only with the mode switch request code sequence 1030.Therefore, the MS 1002 switches to the EFCH mode when the duration K1020 ends, and then transmits feedback information through the feedbackchannel of the EFCH mode. In this case, the BS 1004 determines whether amode switch request of the MS 1002 is permitted, and if it is permitted,transmits feedback channel allocation information 1040. The feedbackchannel allocation information 1040 includes information indicating afeedback channel location, a feedback period, a feedback mode, etc. Thatis, when the feedback channel allocation information 1040 is used, thefeedback channel location may vary. Upon receiving the feedback channelallocation information 1040, the MS 1002 switches to the BFCH mode, andperiodically transmits feedback information through the feedback channelof the BFCH mode. Herein, a feedback period of the BFCH mode and afeedback period of the EFCH mode may be substantially identical to ordifferent from each other.

FIG. 11 illustrates a process of periodically switching to a BFCH modewhile temporarily switching from an EFCH mode to the BFCH mode by usingan indicator of the EFCH mode in a broadband wireless communicationsystem according to an exemplary embodiment of the present invention.

Referring to FIG. 11, an MS 1102 transmits feedback information to a BS1104 through a feedback channel of the EFCH mode. While operating in theEFCH mode, an MS 1102 periodically switches to the BFCH mode. Aninterval of periodical switching to the BFCH mode is defined as thenumber of frames or the number of feedback attempts. In addition, alength of a duration in which the BFCH mode is maintained wheneverswitching to the BFCH mode occurs is defined as the number of frames orthe number of feedback attempts. For example, the periodic switching tothe BFCH mode may be defined as one feedback attempt every 128 frames.In addition, the exemplary embodiment of FIG. 11 allows temporarilyswitching to the BFCH mode when mode switching is requested through afeedback channel of the EFCH mode. Accordingly, while operating in theEFCH mode, the MS 1102 determines switching to the BFCH mode andtransmits feedback information including a mode switch request 1110through the feedback channel of the EFCH mode. For example, the modeswitching request implies an activated mode switch indication bit ofFIG. 4 above. That is, an indicator indicating the mode switch requestis included in the feedback information transmitted according to theEFCH mode, and the indicator is set to an activated value if modeswitching is requested, and is set to an inactivated value if modeswitching is not requested. However, the feedback informationtransmitted according to the EFCH mode may have various formats, and inthis case, feedback information of all formats may include theindicator, or only feedback information of some formats may include theindicator. Thereafter, the MS 1102 switches to the BFCH mode,periodically transmits feedback information through a feedback channelof the BFCH mode during a duration K 1120, and returns to the EFCH mode.

As described above, the exemplary embodiments of the present inventionwith reference to FIG. 5 to FIG. 11 assume a single EFCH mode. Accordingto another exemplary embodiment of the present invention, a plurality ofEFCH modes including different parameter items may exist according to atype of feedback information. In this case, as a mode switch requestcode sequence for requesting switching from the BFCH mode to the EFCHmode, a plurality of code sequences corresponding to the plurality ofEFCH modes can be allocated. In addition, switching from one EFCH modeto another EFCH mode can also be performed. For switching between theEFCH modes, the exemplary embodiments shown in FIG. 7 to FIG. 11 can beused.

Hereinafter, exemplary operations and structures of an MS and a BS foroperating a fast feedback channel will be described with reference tothe accompanying drawings.

FIG. 12 is a flowchart illustrating a process of transmitting feedbackinformation by an MS in a broadband wireless communication systemaccording to an exemplary embodiment of the present invention. It isassumed that a permission of a BS is not necessary for the operation ofthe MS.

Referring to FIG. 12, the MS determines whether it is time fortransmitting feedback information in step 1201. Since the MSperiodically transmits the feedback information through a fast feedbackchannel allocated by the BS, the MS determines whether one periodelapses after the feedback information is transmitted previously.

If it is determined that it is time for transmitting the feedbackinformation, the MS generates the feedback information in step 1203. Thefeedback information includes at least one of items, i.e., CQI, apreferred sub-band index, a PMI or rank for a MIMO mode. In this case,the item included in the feedback information is determined by a Signalto Noise Ratio (SNR) of a downlink channel. More items may be includedwhen a channel condition allows. In addition, a mode of a fast feedbackchannel is determined according to the items included in the feedbackinformation.

After generating the feedback information, the MS determines whether atransmission type of the feedback information conforms to a BFCH mode oran EFCH mode in step 1205. That is, the MS determines whether thefeedback information generated in step 1203 is feedback information tobe transmitted to a BFCH or feedback information to be transmitted to anEFCH.

If it is determined that the transmission type of the feedbackinformation conforms to the BFCH mode in step 1205, the MS determineswhether the fast feedback channel currently operates in the BFCH mode instep 1207. That is, the MS determines whether the mode of the fastfeedback channel needs to be switched. If it is determined that the fastfeedback channel currently operates the BFCH mode, the MS proceeds tostep 1211.

In contrast, if it is determined that the fast feedback channel does notcurrently operate in the BFCH mode, the MS transmits a code forswitching to the BFCH mode or a bit-stream including an activated modeswitch indication bit in step 1209. Herein, the code for switching tothe BFCH mode is one of code sequences transmitted through the BFCH, andthe bit-stream including the activated mode switch indication bit is abit-stream transmitted through the EFCH. Therefore, when transmittingthe code for switching to the BFCH mode, the MS configures and transmitsthe BFCH, and when transmitting the bit-stream including the activatedmode switch indication bit, the MS configures and transmits the EFCH. Inthis case, which one will be transmitted between the code for switchingto the BFCH mode or the bit-stream including the activated mode switchindication bit may differ according to an exemplary embodiment of thepresent invention.

In step 1211, the MS selects a code sequence corresponding to thefeedback information generated in step 1203. In other words, the MSselects a payload corresponding to the feedback information, and selectsa code sequence corresponding to the payload from code sequences for theBFCH.

After selecting the code sequence, the MS configures the BFCH by usingthe code sequence and transmits the BFCH in step 1213. That is, the MSgenerates a feedback signal to be transmitted through the fast feedbackchannel according to a coherent modulation scheme. More specifically,the MS converts the code sequence into complex symbols, and configuresthe BFCH by assigning the complex symbols according to a structure ofthe BFCH. Further, the MS transmits the BFCH by using a resourceallocated for the fast feedback channel.

If the transmission type of the feedback information conforms to theEFCH mode in step 1205, the MS determines whether the fast feedbackchannel currently operates in the EFCH mode in step 1217. That is, theMS determines whether the mode of the fast feedback channel needs to beswitched. If the fast feedback channel currently operates in the EFCHmode, the MS proceeds to step 1221.

In contrast, if it is determined that the fast feedback channel does notcurrently operate in the EFCH mode, the MS transmits the code forswitching to the EFCH mode in step 1219. The code for switching to theEFCH mode is one of code sequences transmitted through the EFCH.Therefore, the MS configures and transmits the EFCH by using the codefor switching to the EFCH mode.

In step 1221, the MS performs coding and modulation on the feedbackinformation generated in step 1203. In other words, the MS generatescomplex symbols to be transmitted through the EFCH by coding andmodulating the feedback information.

After coding and modulating the feedback information, the MS configuresthe EFCH by using the complex symbols and then transmits the EFCH instep 1223. That is, the MS generates a feedback signal to be transmittedthrough the fast feedback channel according to the coherent modulationscheme. In other words, the MS configures the EFCH by assigning thecomplex symbols and pilot symbols according to a structure of the EFCH.Then, the MS transmits the EFCH by using a resource allocated for thefast feedback channel.

FIG. 13 is a flowchart illustrating a process of transmitting feedbackinformation by a BS in a broadband wireless communication systemaccording to an exemplary embodiment of the present invention. In FIG.13, the BS receives feedback information for a single MS. If the BScommunicates with a plurality of MSs, the processes of FIG. 13 may beconcurrently performed as many as the number of the MSs. It is assumedthat a permission of the BS is not necessary for the operation of theMS.

Referring to FIG. 13, the BS determines whether fast feedbackinformation is received in step 1301. That is, the BS determines whetherfeedback information is received through a fast feedback channel.

Upon receiving the feedback information, the BS determines whether thefast feedback channel currently operates in a BFCH mode or an EFCH modein step 1303. That is, the BS determines a demodulation scheme of thesignal received through the fast feedback channel.

If it is determined that the fast feedback channel currently operates inthe BFCH mode, the BS detects a Transmit (Tx) code sequence by usingcorrelation values between each of candidate code sequences and thereceived signal in step 1305. That is, the BS detects the Tx codesequence from the signal received through the fast feedback channelaccording to a noncoherent demodulation scheme. More specifically, theBS calculates correlation values between each of available codesequences and the received signal. In this case, the BS calculatescorrelation values for each of a plurality of tiles and then performs asquare operation on each correlation value. Further, the BS adds thesquared correlation values calculated using the same candidate codesequence from the correlation values calculated from each tile, and thensearches for a candidate code sequence corresponding to a maximum sum ofthe squared correlation values.

After detecting the code sequence, the BS determines whether thedetected code sequence is an E1 code in step 1307. In other words, theBS determines whether the detected code sequence is for switching to theEFCH mode. In this case, according to another exemplary embodiment ofthe present invention, the code sequence for switching to the EFCH modemay be not the E1 code but a code sequence that indicates a preferredMIMO mode using the EFCH mode.

If it is determined that the detected code sequence is not the E1 codein step 1307, the BS evaluates the feedback information from thedetected code sequence in step 1309. In other words, the BS evaluates apayload corresponding to the detected code sequence, and then evaluatesthe feedback information corresponding to the payload. For example, theBS evaluates a CQI of the MS by using the feedback information.

In contrast, if it is determined that the detected code sequence is theE1 code in step 1307, the BS determines switching to the fast feedbackchannel to the EFCH mode in a next frame in step 1311. Accordingly, inthe next frame, the BS detects feedback information according to theEFCH mode.

If it is determined that the fast feedback channel currently operates inthe EFCH mode in step 1303, the BS detects a feedback bit-stream byperforming channel estimation, demodulation, and decoding in step 1313.That is, the BS detects a feedback bit-stream from the signal receivedthrough the fast feedback channel according to the coherent demodulationscheme. More specifically, the BS extracts pilot symbols from the signalreceived through the fast feedback channel, and then estimates achannel. Thereafter, the BS compensates for channel distortion ofinformation symbols by using the estimated channel, and performsdemodulation and decoding on the information symbols.

After detecting the feedback bit-stream, the BS evaluates whether anerror occurs in the detected feedback bit-stream in step 1315. Forexample, the BS determines the occurrence of error by performing CyclicRedundancy Check (CRC) processing, reliability estimation on channeldecoding, etc.

If it is determined that there is no error in step 1315, the BSevaluates the feedback information in step 1317. In other words, the BSdivides the feedback bit-streams into an information bit-stream and amode switch indication bit, and evaluates the feedback informationincluded in the information bit-stream. For example, the BS evaluates aCQI, a preferred sub-band, a PMI, a rank, etc., of the MS by using thefeedback information.

After evaluating the feedback information, the BS determines whether themode switch indication bit is activated in step 1319. In other words,the BS determines whether the mode switch indication bit is set to ‘1’.That is, the BS determines whether switching to the BFCH mode isrequested from the MS. If it is determined that the mode switchindication bit is activated in step 1319, the BS proceeds to step 1325.

If it is determined that an error occurs in step 1315, the BS detects aTx code sequence by using correlation values between each of candidatecode sequences and the received signal in step 1321. More specifically,the BS calculates correlation values between each of available codesequences and the received signal. In this case, the BS calculatescorrelation values for each of a plurality of tiles and then performs asquare operation on each correlation value. Further, the BS adds thesquared correlation values calculated using the same candidate codesequence from the correlation values calculated from each tile, and thensearches for a candidate code sequence corresponding to a maximum sum ofthe squared correlation values.

After detecting the code sequence, the BS determines whether thedetected code sequence is an E2 code in step 1323. In other words, theBS determines whether the detected code sequence is for switching to theBFCH mode. That is, the BS determines whether switching to the BFCH modeis requested from the MS. According to another exemplary embodiment ofthe present invention, whether switching to the BFCH mode is requestedcan be determined according to whether a code sequence indicating apreferred MIMO mode is received. In this case, the BS determines whetherthe code sequence indicating the preferred MIMO mode is received.

In contrast, if it is determined that the detected code sequence is theE2 code in step 1323, the BS determines to switch the fast feedbackchannel to the BFCH mode in a next frame in step 1325. Accordingly, inthe next frame, the BS detects feedback information according to theBFCH mode.

In the process of operating the BS as shown in FIG. 13, the BS attemptsto detect the E2 code for switching to the BFCH mode and also attemptsto detect whether the mode switch indication bit is activated. However,according to an exemplary embodiment of the present invention, step 1321and step 1323 may be omitted when the BS does not attempt to detect theE2 code for switching to the BFCH mode, or step 1319 may be omitted whenthe BS does not attempt to detect whether the mode switch indication bitis activated.

FIG. 14 is a flowchart illustrating an operation of an MS for switchingfrom a BFCH mode to an EFCH mode under the control of a BS in abroadband wireless communication system according to an exemplaryembodiment of the present invention.

Referring to FIG. 14, the MS determines whether it is time fortransmitting feedback information in step 1401. Since the MSperiodically transmits the feedback information through a fast feedbackchannel allocated by the BS, the MS determines whether one periodelapses after the feedback information is transmitted previously. Theperiod is determined according to a mode of the feedback channel. Thefeedback channel of the MS currently operates in the BFCH mode.

If it is determined that it is time for transmitting the feedbackinformation in step 1401, the MS transmits the feedback informationaccording to the BFCH mode in step 1403. More specifically, the MSgenerates the feedback information, and selects a code sequencecorresponding to the feedback information. Further, the MS converts thecode sequence into complex symbols, and transmits the complex symbolsthrough the feedback channel of the BFCH mode. Thereafter, the MSreturns to step 1401.

If it is determined that it is not time for transmitting the feedbackinformation in step 1401, the MS determines whether switching to theEFCH mode is necessary in step 1405. The switching to the EFCH mode isdetermined according to changes in a type of the feedback information.The type of the feedback information is determined according to acommunication mode. For example, when intending to operate in a MIMOmode, the MS determines switching to the EFCH mode. If the switching tothe EFCH mode is not necessary, the MS returns to step 1401.

In contrast, if it is determined that the switching to the EFCH mode isnecessary in step 1405, the MS transmits a mode switch request codesequence of the BFCH mode in step 1407. In other words, the MS selects acode sequence assigned for a mode switch request from a plurality oftransmissible code sequences in the BFCH mode, converts the codesequence into complex symbols, and transmits the complex symbols throughthe feedback channel of the BFCH mode. For example, the mode switchrequest code sequence is either an E1 code dedicatedly allocated forswitching from the BFCH mode to the EFCH mode or a code sequenceindicating a preferred MIMO mode using the EFCH mode to be switched.

In step 1409, the MS determines whether it is time for transmittingfeedback information. Since the MS periodically transmits the feedbackinformation through the fast feedback channel allocated by the BS, theMS determines whether one period elapses after the feedback informationis transmitted previously. The period is determined according to themode of the feedback channel. Since there is no permission from the BSafter transmitting the mode switch request code sequence, the feedbackchannel currently operates in the BFCH mode.

If it is determined that it is time for transmitting the feedbackinformation in step 1409, the MS transmits the feedback informationaccording to the BFCH mode in step 1411. More specifically, the MSgenerates the feedback information, and selects a code sequencecorresponding to the feedback information. Further, the MS converts thecode sequence into complex symbols, and transmits the complex symbolsthrough the feedback channel operating in the BFCH mode. Thereafter, theMS returns to step 1409.

If it is determined that it is not time for transmitting the feedbackinformation in step 1409, the MS determines whether feedback channelallocation information for permitting switching to the EFCH is receivedin step 1413. The feedback channel allocation information includesinformation indicating a feedback channel location, a feedback period, afeedback mode, etc. In this case, the feedback channel allocationinformation includes information for allocating a feedback channel ofthe EFCH mode.

Upon receiving the feedback channel allocation information, the MSdetermines whether it is time for transmitting feedback information instep 1415. Since the MS periodically transmits the feedback informationthrough the fast feedback channel allocated by the BS, the MS determineswhether one period elapses after the feedback information is transmittedpreviously. The period is determined according to the mode of thefeedback channel. Since switching to the EFCH mode is permitted by theBS, the feedback channel currently operates in the BFCH mode.

If it is determined that it is time for transmitting the feedbackinformation in step 1415, the MS transmits the feedback informationaccording to the EFCH mode in step 1417. More specifically, the MSgenerates the feedback information, and generates complex symbols to betransmitted through the EFCH by coding and modulating the feedbackinformation. Further, the MS transmits the complex symbols and pilotsymbols through the feedback channel of the EFCH mode.

FIG. 15 is a flowchart illustrating an operation of a BS for controllingswitching from a BFCH mode to an EFCH mode in a broadband wirelesscommunication system according to an exemplary embodiment of the presentinvention.

Referring to FIG. 15, the BS determines whether a feedback signal of theBFCH mode is received in step 1501. That is, a feedback channel of acorresponding MS currently operates in the BFCH mode, and the feedbacksignal is periodically received.

Upon receiving the feedback signal of the BFCH mode, the BS detects a Txcode sequence by using correlation value between each of candidate codesequences and the received signal in step 1503. That is, the BS detectsthe Tx code sequence from the signal received through the fast feedbackchannel according to a noncoherent demodulation scheme. Morespecifically, the BS calculates correlation values between each ofavailable code sequences and the received signal. For example, the BScalculates correlation values for each of a plurality of tiles and thenperforms a square operation on each correlation value. Further, the BSadds the squared correlation values calculated using the same candidatecode sequence from the correlation values calculated from each tile, andthen searches for a candidate code sequence corresponding to a maximumsum of the squared correlation values.

After detecting the transmitted code sequence, the BS determines whetherthe detected code sequence is a mode switch request code sequence instep 1505. The mode switch request code sequence implies a code sequenceassigned for a mode switch request from a plurality of transmissiblecode sequences in the BFCH mode. Since the feedback channel currentlyoperates in the BFCH mode, the mode switch request code sequence impliesa code sequence for requesting switching from the BFCH mode to the EFCHmode. For example, the mode switch request code sequence is either an E1code dedicatedly allocated for switching from the BFCH mode to the EFCHmode or a code sequence indicating a preferred MIMO mode using the EFCHmode to be switched.

If it is determined that the detected code sequence is not the modeswitch request code sequence in step 1505, the BS evaluates a codewordcorresponding to the detected code sequence and processes feedbackinformation indicated by the codeword in step 1507. For example, thefeedback information may be a CQI, an event trigger, etc.

In contrast, if the detected code sequence is the mode switch requestcode sequence in step 1505, the BS determines whether mode switching ofthe feedback channel will be permitted in step 1509. Whether to permitthe mode switching is determined by the number of unoccupied feedbackchannels, supportability of an operation of a corresponding mode, etc.If the mode switching of the feedback channel cannot be permitted, theBS returns to step 1501.

In contrast, if it is determined that the mode switching of the feedbackchannel can be permitted in step 1509, the BS transmits feedback channelallocation information for permitting switching to the EFCH mode in step1511. The feedback channel allocation information includes informationindicating a feedback channel location, a feedback period, a feedbackmode, etc. In this case, the feedback channel allocation informationincludes information for allocating the feedback channel of the EFCHmode.

In step 1513, the BS determines whether a feedback signal of the EFCHmode is received. That is, the feedback channel of the MS currentlyoperates in the EFCH mode, and the feedback signal is periodicallyreceived.

Upon receiving the feedback signal of the EFCH mode, the BS determines afeedback bit-stream by performing channel estimation, demodulation, anddecoding in step 1515. That is, the BS detects a feedback bit-streamfrom a signal received through the fast feedback channel according to acoherent demodulation scheme. More specifically, the BS extracts pilotsymbols from the signal received through the fast feedback channel, andthen estimates a channel. Thereafter, the BS compensates for channeldistortion of information symbols by using the estimated channel, andperforms demodulation and decoding on the information symbols.

After detecting the feedback bit-stream, the BS processes feedbackinformation indicated by the detected bit-stream in step 1517. Forexample, the BS evaluates a CQI, a preferred sub-band, a PMI, a rank,etc., by using the feedback information. Thereafter, the BS returns tostep 1513.

FIG. 16 is a flowchart illustrating an operation of an MS fortemporarily switching from an EFCH mode to a BFCH mode in a broadbandwireless communication system according to an exemplary embodiment ofthe present invention.

Referring to FIG. 16, the MS determines whether it is time fortransmitting feedback information in step 1601. Since the MSperiodically transmits the feedback information through a fast feedbackchannel allocated by a BS, the MS determines whether one period elapsesafter the feedback information is transmitted previously. The period isdetermined according to a mode of the feedback channel. The feedbackchannel of the MS currently operates in the EFCH mode.

If it is determined that it is time for transmitting the feedbackinformation in step 1601, the MS transmits the feedback informationaccording to the EFCH mode in step 1603. More specifically, the MSgenerates the feedback information, and generates complex symbols to betransmitted through an EFCH by coding and modulating the feedbackinformation. Further, the MS transmits the complex symbols and pilotsymbols through the feedback channel of the EFCH mode. Therefore, the MSreturns to step 1601.

If it is determined that it is not time for transmitting the feedbackinformation in step 1601, the MS determines whether switching to theBFCH mode is necessary in step 1605. The switching to the BFCH mode isdetermined according to changes in a type of the feedback information.The type of the feedback information is determined according to acommunication mode. For example, when intending to deactivate a MIMOmode while operating in the MIMO mode, the MS determines switching tothe BFCH mode. If the switching to the BFCH mode is not necessary, theMS returns to step 1601.

In contrast, if it is determined that the switching to the BFCH mode isnecessary in step 1605, the MS transmits feedback information includinga mode switch request according to the EFCH mode in step 1607. That is,the MS transmits feedback information according to a transmission periodby appending the mode switch request to the feedback information. Forexample, the mode switch request may be a 1-bit indicator as shown inthe mode switch indication bit 420 of FIG. 4. That is, an indicator thatindicates the mode switch request is included in feedback informationtransmitted according to the EFCH mode, and is set to an activated valueif mode switching is requested and is set to an inactivated value ifmode switching is not requested. However, feedback informationtransmitted according to the EFCH mode may have various formats, and inthis case, feedback information of all formats may include the indicatoror only feedback information of some formats may include the indicator.

In step 1609, the MS determines whether it is time for transmittingfeedback information. Since the MS periodically transmits the feedbackinformation through the fast feedback channel allocated by the BS, theMS determines whether one period elapses after previous feedbackinformation is transmitted. The period is determined according to themode of the feedback channel. Since the feedback information istransmitted according to the EFCH mode including the mode switchrequest, the feedback channel of the MS currently operates in atemporary BFCH mode.

If it is determined that it is time for transmitting the feedbackinformation in step 1609, the MS transmits the feedback informationaccording to the BFCH mode in step 1611. More specifically, the MSgenerates the feedback information, and selects a code sequencecorresponding to the feedback information. Further, the MS converts thecode sequence into complex symbols, and transmits the complex symbolsthrough the feedback channel operating in the BFCH mode. Thereafter, theMS returns to step 1609.

If it is determined that it is not time for transmitting the feedbackinformation in step 1601, the MS determines whether a temporary modeswitch time elapses in step 1613. That is, after transmitting thefeedback information including the mode switch request, the temporarymode switch time starts to elapse, and the MS determines whether thetemporary mode switch time elapses. If the temporary mode switch timedoes not elapse, the MS returns to step 1609. Otherwise, if thetemporary mode switch time elapses, the MS returns to step 1601.

FIG. 17 is a flowchart illustrating an operation of a BS correspondingto an MS for temporarily switching from an EFCH mode to a BFCH mode in abroadband wireless communication system according to an exemplaryembodiment of the present invention.

Referring to FIG. 17, the BS determines whether a feedback signal of theEFCH mode is received in step 1701. That is, a feedback channel of theMS currently operates in the EFCH mode, and the feedback signal isperiodically received.

Upon receiving the feedback signal of the EFCH mode, the BS detects afeedback bit-stream by performing channel estimation, demodulation, anddecoding in step 1703. That is, the BS detects a feedback bit-streamfrom a signal received through the fast feedback channel according to acoherent demodulation scheme. More specifically, the BS extracts pilotsymbols from the signal received through the fast feedback channel, andthen estimates a channel. Thereafter, the BS compensates for channeldistortion of information symbols by using the estimated channel, andperforms demodulation and decoding on the information symbols.

After detecting the feedback bit-stream, the BS determines whether amode switch request is included in the feedback bit-stream in step 1705.The mode switch request is information for reporting a request forswitching from the EFCH mode to the BFCH mode. For example, the modeswitch request may be a 1-bit indicator as shown in the mode switchindication bit 420 of FIG. 4. That is, an indicator that indicates themode switch request is included in feedback information transmittedaccording to the EFCH mode, and is set to an activated value if modeswitching is requested and is set to an inactivated value if modeswitching is not requested. However, feedback information transmittedaccording to the EFCH mode may have various formats, and in this case,feedback information of all formats may include the indicator or onlyfeedback information of some formats may include the indicator.

In contrast, if it is determined that the mode switch request is notincluded in step 1705, the BS processes feedback information indicatedby the detected bit-stream in step 1707. For example, the BS evaluates aCQI, a preferred sub-band, a PMI, a rank, etc., by using the feedbackinformation. Thereafter, the BS returns to step 1701.

In contrast, if it is determined that the mode switch request isincluded in step 1705, the BS determines whether a feedback signal ofthe BFCH mode is received in step 1709. That is, the feedback channel ofthe MS currently operates in a temporary BFCH mode due to the modeswitch request, and the feedback signal is periodically received.

Upon receiving the feedback signal of the BFCH mode in step 1709, the BSdetects a Tx code sequence by using correlation values between each ofcandidate code sequences and the received signal in step 1711. That is,the BS detects the Tx code sequence from the signal received through thefast feedback channel according to a noncoherent demodulation scheme.More specifically, the BS calculates correlation values between each ofavailable code sequences and the received signal. For example, the BScalculates correlation values for each of a plurality of tiles and thenperforms a square operation on each correlation value. Further, the BSadds the squared correlation values calculated using the same candidatecode sequence from the correlation values calculated from each tile, andthen searches for a candidate code sequence corresponding to a maximumsum of the squared correlation values.

In step 1713, the BS evaluates a codeword corresponding to the detectedcode sequence, and processes feedback information indicated by thecodeword. For example, the feedback information may be a CQI, an eventtrigger, etc.

If it is determined that the feedback signal of the BFCH mode is notreceived in step 1709, the BS determines whether a temporary mode switchtime elapses in step 1715. That is, after transmitting the feedbackinformation including the mode switch request, the temporary mode switchtime starts to elapse, and the BS determines whether the temporary modeswitch time elapses. If the temporary mode switch time does not elapse,the BS returns to step 1709. Otherwise, if the temporary mode switchtime elapses, the BS returns to step 1701.

FIG. 18 is a flowchart illustrating an operation of an MS for switchingto a temporary BFCH mode and for requesting switching to a BFCH modefrom the temporary BFCH mode in a broadband wireless communicationsystem according to an exemplary embodiment of the present invention.

Referring to FIG. 18, the MS determines whether it is time fortransmitting feedback information in step 1801. Since the MSperiodically transmits the feedback information through a fast feedbackchannel allocated by a BS, the MS determines whether one period elapsesafter the feedback information is transmitted previously. The period isdetermined according to a mode of the feedback channel. The feedbackchannel currently operates in the EFCH mode.

If it is determined that it is time for transmitting the feedbackinformation in step 1801, the MS transmits the feedback informationaccording to the EFCH mode in step 1803. More specifically, the MSgenerates the feedback information, and generates complex symbols to betransmitted through an EFCH by coding and modulating the feedbackinformation. Further, the MS transmits the complex symbols and pilotsymbols through the feedback channel of the EFCH mode. Thereafter, theMS returns to step 1801.

If it is determined that it is not time for transmitting the feedbackinformation in step 1801, the MS determines whether switching to theBFCH mode is necessary in step 1805. The switching to the BFCH mode isdetermined according to changes in a type of the feedback information.The type of the feedback information is determined according to acommunication mode. For example, when intending to deactivate a MIMOmode while operating in the MIMO mode, the MS determines switching tothe BFCH mode. If the switching to the BFCH mode is not necessary, theMS returns to step 1801.

In contrast, if it is determined that the switching to the BFCH mode isnecessary in step 1805, the MS transmits feedback information includinga mode switch request according to the EFCH mode in step 1807. That is,the MS transmits feedback information according to a transmission periodby appending the mode switch request to the feedback information. Forexample, the mode switch request may be a 1-bit indicator as shown inthe mode switch indication bit 420 of FIG. 4. That is, an indicator thatindicates the mode switch request is included in feedback informationtransmitted according to the EFCH mode, and is set to an activated valueif mode switching is requested and is set to an inactivated value ifmode switching is not requested. However, feedback informationtransmitted according to the EFCH mode may have various formats, and inthis case, feedback information of all formats may include the indicatoror only feedback information of some formats may include the indicator.

In step 1809, the MS determines whether it is time for transmittingfeedback information. Since the MS periodically transmits the feedbackinformation through the fast feedback channel allocated by the BS, theMS determines whether one period elapses after previous feedbackinformation is transmitted. The period is determined according to themode of the feedback channel. Since the feedback information istransmitted at present according to the EFCH mode including the modeswitch request, the feedback channel of the MS operates in the temporaryBFCH mode.

If it is determined that it is time for transmitting the feedbackinformation in step 1809, the MS transmits a mode switch request codesequence of the BFCH mode in step 1811. In other words, the MS selects acode sequence assigned for a mode switch request from a plurality oftransmissible code sequences in the BFCH mode, converts the codesequence into complex symbols, and transmits the complex symbols throughthe feedback channel of the BFCH mode. For example, the mode switchrequest code sequence is either an E1 code dedicatedly allocated forswitching from the BFCH mode to the EFCH mode or a code sequenceindicating a preferred MIMO mode using the EFCH mode to be switched.

In step 1813, the MS determines whether it is time for transmittingfeedback information. Since the MS periodically transmits the feedbackinformation through the fast feedback channel allocated by the BS, theMS determines whether one period elapses after the feedback informationis transmitted previously. The period is determined according to themode of the feedback channel. Since the feedback information istransmitted according to the EFCH mode including the mode switchrequest, the feedback channel of the MS currently operates in thetemporary BFCH mode.

If it is determined that it is not time for transmitting the feedbackinformation in step 1813, the MS determines whether feedback channelallocation information for permitting switching to the BFCH mode isreceived from the BS in step 1815. The feedback channel allocationinformation includes information indicating a feedback channel location,a feedback period, a feedback mode, etc. In this case, the feedbackchannel allocation information includes information for allocating thefeedback channel of the BFCH mode.

If it is determined that the feedback channel allocation information isnot received in step 1815, the MS determines whether a temporary modeswitch time elapses in step 1817. That is, after transmitting thefeedback information including the mode switch request, the temporarymode switch time starts to elapse, and the MS determines whether thetemporary mode switch time elapses. If the temporary mode switch timedoes not elapse, the MS returns to step 1813.

That is, by repeating steps 1813 to 1817, the MS determines whether thefeedback information transmission time arrives, whether the feedbackchannel allocation information is received, or whether the temporarymode switch time elapses. If the feedback information transmission timearrives before the feedback channel allocation information is receivedor before the temporary mode switch time elapses in step 1813, the MStransmits feedback information according to the BFCH mode in step 1819.More specifically, the MS generates the feedback information, andselects a code sequence corresponding to the feedback information.Further, the MS converts the code sequence into complex symbols, andtransmits the complex symbols through the feedback channel operating inthe BFCH mode. Thereafter, the MS returns to step 1813.

In contrast, if the feedback channel allocation information forpermitting switching to the BFCH mode is received before the temporarymode switch time elapses in step 1815, the MS determines whether it istime for transmitting feedback information in step 1821. Since the MSperiodically transmits the feedback information through the fastfeedback channel allocated by the BS, the MS determines whether oneperiod elapses after the feedback information is transmitted previously.The period is determined according to the mode of the feedback channel.Since the feedback channel allocation information for permittingswitching to the BFCH mode is received, the feedback channel of the MScurrently operates in the BFCH mode.

Upon arrival of the time for transmitting the feedback information, theMS transmits the feedback information according to the BFCH mode in step1823. More specifically, the MS generates the feedback information, andselects a code sequence corresponding to the feedback information.Further, the MS converts the code sequence into complex symbols, andtransmits the complex symbols through the feedback channel operating inthe BFCH mode. Thereafter, the MS returns to step 1801.

If the temporary mode switch time elapses before the feedback channelallocation information is received in step 1817, the MS determineswhether it is time for transmitting feedback information in step 1825.Since the MS periodically transmits the feedback information through afast feedback channel allocated by a BS, the MS determines whether oneperiod elapses after the feedback information is transmitted previously.The period is determined according to a mode of the feedback channel.Since the temporary mode switch time elapses, the feedback channel ofthe MS currently operates in the EFCH mode.

If it is determined that it is time for transmitting the feedbackinformation in step 1825, the MS transmits the feedback informationaccording to the EFCH mode in step 1827. More specifically, the MSgenerates the feedback information, and generates complex symbols to betransmitted through an EFCH by coding and modulating the feedbackinformation. Further, the MS transmits the complex symbols and pilotsymbols through the feedback channel of the EFCH mode.

After transmitting the feedback information according to the EFCH mode,or if it is not time for transmitting the feedback information, the MSdetermines whether feedback channel allocation information forpermitting switching to the BFCH mode is received from the BS in step1829. The feedback channel allocation information includes informationindicating a feedback channel location, a feedback period, a feedbackmode, etc. In this case, the feedback channel allocation informationincludes information for allocating the feedback channel of the BFCHmode. If the feedback channel allocation information is received,returning to step 1821, the MS uses the feedback channel in the BFCHmode. Otherwise, if the feedback channel allocation information is notreceived, the MS returns to step 1825.

FIG. 19 is a flowchart illustrating an operation of a BS correspondingto an MS for switching to a temporary BFCH mode and for requestingswitching to a BFCH mode from the temporary BFCH mode in a broadbandwireless communication system according to an exemplary embodiment ofthe present invention.

Referring to FIG. 19, the BS determines whether a feedback signal of theEFCH mode is received in step 1901. That is, the feedback channel of theMS currently operates in the EFCH mode, and the feedback signal isperiodically received.

Upon receiving the feedback signal of the EFCH mode, the BS determines afeedback bit-stream by performing channel estimation, demodulation, anddecoding in step 1903. That is, the BS detects a feedback bit-streamfrom a signal received through the fast feedback channel according to acoherent demodulation scheme. More specifically, the BS extracts pilotsymbols from the signal received through the fast feedback channel, andthen estimates a channel. Thereafter, the BS compensates for channeldistortion of information symbols by using the estimated channel, andperforms demodulation and decoding on the information symbols.

After detecting the feedback bit-stream, the BS determines whether amode switch request is included in the feedback bit-stream in step 1905.The mode switch request is information for reporting a request forswitching from the EFCH mode to the BFCH mode. For example, the modeswitch request may be a 1-bit indicator as shown in the mode switchindication bit 420 of FIG. 4. That is, an indicator that indicates themode switch request is included in feedback information transmittedaccording to the EFCH mode, and is set to an activated value if modeswitching is requested and is set to an inactivated value if modeswitching is not requested. However, feedback information transmittedaccording to the EFCH mode may have various formats, and in this case,feedback information of all formats may include the indicator or onlyfeedback information of some formats may include the indicator.

In contrast, if it is determined that the mode switch request is notincluded in step 1905, the BS processes feedback information indicatedby the detected bit-stream in step 1907. For example, the BS evaluates aCQI, a preferred sub-band, a PMI, a rank, etc., by using the feedbackinformation. Thereafter, the BS returns to step 1901.

In contrast, if it is determined that the mode switch request isincluded in step 1905, the BS determines whether a feedback signal ofthe BFCH mode is received in step 1909. That is, the feedback channel ofthe MS currently operates in the temporary BFCH mode due to the modeswitch request, and the feedback signal is periodically received.

If it is determined that the feedback signal of the BFCH mode is notreceived in step 1909, the BS determines whether a temporary mode switchtime elapses in step 1911. That is, after transmitting the feedbackinformation including the mode switch request, the temporary mode switchtime starts to elapse, and the BS determines whether the temporary modeswitch time elapses. If the temporary mode switch time does not elapse,the BS returns to step 1909. Otherwise, if the temporary mode switchtime elapses, the BS returns to step 1901.

Upon receiving the feedback signal of the BFCH mode in step 1909, the BSdetects a Tx code sequence by using correlation value between each ofcandidate code sequences and the received signal in step 1913. That is,the BS detects the Tx code sequence from the signal received through thefast feedback channel according to a noncoherent demodulation scheme.More specifically, the BS calculates correlation values between each ofavailable code sequences and the received signal. For example, the BScalculates correlation values for each of a plurality of tiles and thenperforms a square operation on each correlation value. Further, the BSadds the squared correlation values calculated using the same candidatecode sequence from the correlation values calculated from each tile, andthen searches for a candidate code sequence corresponding to a maximumsum of the squared correlation values.

In step 1915, the BS determines whether the detected code sequence is amode switch request code sequence. The mode switch request code sequenceimplies a code sequence assigned for a mode switch request from aplurality of transmissible code sequences in the BFCH mode. The modeswitch request code sequence implies a code sequence for requestingswitching from the EFCH mode to the BFCH mode. For example, the modeswitch request code sequence is either an E2 code dedicatedly allocatedfor switching from the EFCH mode to the BFCH mode or a code sequenceindicating a preferred MIMO mode using the BFCH mode.

If it is determined that the detected code sequence is not the modeswitch request code sequence in step 1915, the BS evaluates a codewordcorresponding to the detected code sequence and processes feedbackinformation indicated by the codeword in step 1917. For example, thefeedback information may be a CQI, an event trigger, etc.

In contrast, if it is determined that the detected code sequence is themode switch request code sequence in step 1915, the BS determineswhether mode switching of the feedback channel will be permitted in step1919. Whether to permit the mode switching is determined by the numberof unoccupied feedback channels, supportability of an operation of acorresponding mode, etc. If the mode switching of the feedback channelcannot be permitted, the BS returns to step 1909.

If it is determined that the mode switching of the feedback channel canbe permitted in step 1919, the BS transmits feedback channel allocationinformation for permitting switching to the BFCH mode in step 1921. Thefeedback channel allocation information includes information indicatinga feedback channel location, a feedback period, a feedback mode, etc. Inthis case, the feedback channel allocation information includesinformation for allocating the feedback channel of the BFCH mode.

In step 1923, the BS determines whether a feedback signal of the BFCHmode is received. That is, the feedback channel of the MS currentlyoperates in the BFCH mode since the mode switching is permitted, and thefeedback signal is periodically received.

Upon receiving the feedback signal of the BFCH mode, the BS detects a Txcode sequence by using correlation values between each of candidate codesequences and the received signal in step 1925. That is, the BS detectsthe Tx code sequence from the signal received through the fast feedbackchannel according to the noncoherent demodulation scheme. Morespecifically, the BS calculates correlation values between each ofavailable code sequences and the received signal. For example, the BScalculates correlation values for each of a plurality of tiles and thenperforms a square operation on each correlation value. Further, the BSadds the squared correlation values calculated using the same candidatecode sequence from the correlation values calculated from each tile, andthen searches for a candidate code sequence corresponding to a maximumsum of the squared correlation values.

After detecting the code sequence, the BS evaluates a codewordcorresponding to the detected code sequence, and processes feedbackinformation indicated by the codeword in step 1927. For example, thefeedback information may be a CQI, an event trigger, etc. Thereafter,the BS returns to step 1923.

FIG. 20 is a flowchart illustrating an operation of an MS for requestingswitching to a temporary BFCH mode while periodically switching to aBFCH mode in a broadband wireless communication system according to anexemplary embodiment of the present invention.

Referring to FIG. 20, the MS determines whether it is time fortransmitting feedback information in step 2001. Since the MSperiodically transmits the feedback information through a fast feedbackchannel allocated by a BS, the MS determines whether one period elapsesafter the feedback information is transmitted previously. The period isdetermined according to a mode of the feedback channel. The feedbackchannel currently operates in an EFCH mode.

If it is determined that it is time for transmitting the feedbackinformation in step 2001, the MS transmits the feedback informationaccording to the EFCH mode in step 2003. More specifically, the MSgenerates the feedback information, and generates complex symbols to betransmitted through an EFCH by coding and modulating the feedbackinformation. Further, the MS transmits the complex symbols and pilotsymbols through the feedback channel of the EFCH mode. Thereafter, theMS returns to step 2001.

If it is determined that it is not time for transmitting the feedbackinformation in step 2001, the MS determines whether a BFCH mode switchperiod arrives in step 2005. That is, the MS switches to the BFCH modeaccording to a specific period. The BFCH mode switch period isdetermined by the number of frames or the number of feedback attempts.

Upon arrival of the BFCH mode switch period, the MS transmits feedbackinformation according to the BFCH mode in step 2007. More specifically,the MS generates the feedback information, and selects a code sequencecorresponding to the feedback information. Further, the MS converts thecode sequence into complex symbols, and transmits the complex symbolsthrough the feedback channel of the BFCH mode. Thereafter, the MSreturns to step 2001.

If it is determined that the BFCH mode switch period does not arrive instep 2005, the MS determines whether switching to the BFCH mode isnecessary in step 2009. The switching to the BFCH mode is determinedaccording to changes in a type of the feedback information. The type ofthe feedback information is determined according to a communicationmode. For example, when intending to deactivate a MIMO mode whileoperating in the MIMO mode, the MS determines switching to the BFCHmode. If the switching to the BFCH mode is not necessary, the MS returnsto step 2001.

In contrast, if it is determined that the switching to the BFCH mode isnecessary in step 2009, the MS transmits feedback information includinga mode switch request according to the EFCH mode in step 2011. That is,the MS transmits feedback information according to a transmission periodby appending the mode switch request to the feedback information. Forexample, the mode switch request may be a 1-bit indicator as shown inthe mode switch indication bit 420 of FIG. 4. That is, an indicator thatindicates the mode switch request is included in feedback informationtransmitted according to the EFCH mode, and is set to an activated valueif mode switching is requested and is set to an inactivated value ifmode switching is not requested. However, feedback informationtransmitted according to the EFCH mode may have various formats, and inthis case, feedback information of all formats may include the indicatoror only feedback information of some formats may include the indicator.

In step 2013, the MS determines whether it is time for transmittingfeedback information. Since the MS periodically transmits the feedbackinformation through the fast feedback channel allocated by the BS, theMS determines whether one period elapses after previous feedbackinformation is transmitted. The period is determined according to themode of the feedback channel. Since the feedback information istransmitted at present according to the EFCH mode including the modeswitch request, the feedback channel of the MS currently operates in thetemporary BFCH mode.

If it is determined that it is time for transmitting the feedbackinformation in step 2013, the MS transmits the feedback informationaccording to the BFCH mode in step 2015. More specifically, the MSgenerates the feedback information, and selects a code sequencecorresponding to the feedback information. Further, the MS converts thecode sequence into complex symbols, and transmits the complex symbolsthrough the feedback channel operating in the BFCH mode. Thereafter, theMS returns to step 2013.

If it is determined that it is not time for transmitting the feedbackinformation in step 2013, the MS determines whether a temporary modeswitch time elapses in step 2017. That is, after transmitting thefeedback information including the mode switch request, the temporarymode switch time starts to elapse, and the MS determines whether thetemporary mode switch time elapses. If the temporary mode switch timedoes not elapse, the MS returns to step 2013. Otherwise, if thetemporary mode switch time elapses, the MS returns to step 2001.

FIG. 21 is a flowchart illustrating an operation of a BS correspondingto an MS for requesting switching to a temporary BFCH mode whileperiodically switching to a BFCH mode in a broadband wirelesscommunication system according to an exemplary embodiment of the presentinvention.

Referring to FIG. 21, the BS determines whether a BFCH mode switchperiod arrives in step 2101. That is, a mode of the feedback channel ofthe MS switches to the BFCH mode according to a specific period. TheBFCH mode switch period is determined by the number of frames or thenumber of feedback attempts.

Upon arrival of the BFCH mode switch period in step 2101, the BSdetermines whether a feedback signal of the BFCH mode is received instep 2103. That is, the feedback channel of the MS currently operates ina periodic BFCH mode.

Upon receiving the feedback signal of the BFCH mode, the BS detects a Txcode sequence by using correlation values between each of candidate codesequences and the received signal in step 2105. That is, the BS detectsthe Tx code sequence from the signal received through the fast feedbackchannel according to a noncoherent demodulation scheme. Morespecifically, the BS calculates correlation values between each ofavailable code sequences and the received signal. For example, the BScalculates correlation values for each of a plurality of tiles and thenperforms a square operation on each correlation value. Further, the BSadds the squared correlation values calculated using the same candidatecode sequence from the correlation values calculated from each tile, andthen searches for a candidate code sequence corresponding to a maximumsum of the squared correlation values.

In step 2107, the BS evaluates a codeword corresponding to the detectedcode sequence, and processes feedback information indicated by thecodeword. For example, the feedback information may be a CQI, an eventtrigger, etc. Thereafter, the BS returns to step 2101.

If it is determined that the BFCH mode switch period does not arrive instep 2101, the BS determines whether a feedback signal of the EFCH modeis received in step 2109. That is, the feedback channel of the MScurrently operates in the EFCH mode, and the feedback signal isperiodically received.

Upon receiving the feedback signal of the EFCH mode, the BS determines afeedback bit-stream by performing channel estimation, demodulation, anddecoding in step 2111. That is, the BS detects a feedback bit-streamfrom a signal received through the fast feedback channel according to acoherent demodulation scheme. More specifically, the BS extracts pilotsymbols from the signal received through the fast feedback channel, andthen estimates a channel. Thereafter, the BS compensates for channeldistortion of information symbols by using the estimated channel, andperforms demodulation and decoding on the information symbols.

After detecting the feedback bit-stream in step 2111, the BS determineswhether a mode switch request is included in the feedback bit-stream instep 2113. The mode switch request is information for reporting arequest for switching from the EFCH mode to the BFCH mode. For example,the mode switch request may be a 1-bit indicator as shown in the modeswitch indication bit 420 of FIG. 4. That is, an indicator thatindicates the mode switch request is included in feedback informationtransmitted according to the EFCH mode, and is set to an activated valueif mode switching is requested and is set to an inactivated value ifmode switching is not requested. However, feedback informationtransmitted according to the EFCH mode may have various formats, and inthis case, feedback information of all formats may include the indicatoror only feedback information of some formats may include the indicator.

In contrast, if it is determined that the mode switch request is notincluded in step 2113, the BS processes feedback information indicatedby the detected bit-stream in step 2115. For example, the BS evaluates aCQI, a preferred sub-band, a PMI, a rank, etc., by using the feedbackinformation. Thereafter, the BS returns to step 2101.

In contrast, if it is determined that the mode switch request isincluded in step 2113, the BS determines whether a feedback signal ofthe BFCH mode is received in step 2117. That is, the feedback channel ofthe MS operates in the temporary BFCH mode due to the mode switchrequest, and the feedback signal is periodically received.

Upon receiving the feedback signal of the BFCH mode, the BS detects a Txcode sequence by using correlation value between each of candidate codesequences and the received signal in step 2119. That is, the BS detectsthe Tx code sequence from the signal received through the fast feedbackchannel according to the noncoherent demodulation scheme. Morespecifically, the BS calculates correlation values between each ofavailable code sequences and the received signal. For example, the BScalculates correlation values for each of a plurality of tiles and thenperforms a square operation on each correlation value. Further, the BSadds the squared correlation values calculated using the same candidatecode sequence from the correlation values calculated from each tile, andthen searches for a candidate code sequence corresponding to a maximumsum of the squared correlation values.

In step 2121, the BS evaluates a codeword corresponding to the detectedcode sequence, and processes feedback information indicated by thecodeword. For example, the feedback information may be a CQI, an eventtrigger, etc.

If it is determined that the feedback signal of the BFCH mode is notreceived in step 2117, the BS determines whether a temporary mode switchtime elapses in step 2123. That is, after transmitting the feedbackinformation including the mode switch request, the temporary mode switchtime starts to elapse, and the BS determines whether the temporary modeswitch time elapses. If the temporary mode switch time does not elapse,the BS returns to step 2117. Otherwise, if the temporary mode switchtime elapses, the BS returns to step 2101.

FIG. 22A is a block diagram illustrating a structure of an MS in abroadband wireless communication system according to an exemplaryembodiment of the present invention.

Referring to FIG. 22A, the MS includes a Radio Frequency (RF) receiver2202, an OFDM demodulator 2204, a subcarrier dempper 2206, a CQImeasurer 2208, a feedback mode determination unit 2210, a feedbackinformation generator 2212, a BFCH configuration unit 2214, an EFCHconfiguration unit 2216, a subcarrier mapper 2218, an OFDM modulator2220, and an RF transmitter 2222.

The RF receiver 2202 converts an RF signal received through an antennainto a base-band signal. The OFDM demodulator 2204 divides a signalprovided from the RF receiver 2202 in an OFDM symbol unit, removes aCyclic Prefix (CP), and restores complex symbols mapped to a frequencydomain by performing a Fast Fourier Transform (FFT) operation. Thesubcarrier dempper 2206 extracts a signal used for channel qualityestimation, such as a pilot signal, a preamble signal, etc., among thecomplex symbols mapped to the frequency domain. The CQI estimator 2208estimates a downlink CQI by using a signal used for channel qualityestimation such as the pilot signal, the preamble signal, etc.

The feedback mode determination unit 2210 determines a mode of a fastfeedback mode according to channel quality estimated by the CQIestimator 2208. That is, if the CQI is less than a threshold, thefeedback mode determination unit 2210 determines the mode of the fastfeedback mode to a BFCH mode. Otherwise, if the CQI is greater than orequal to the threshold, the feedback mode determination unit 2210determines the mode of the fast feedback mode to an EFCH mode. If themode of the fast feedback channel is determined to the BFCH mode, thefeedback mode determination unit 2210 controls the feedback informationgenerator 2212 to generate feedback information including an itemcorresponding to the BFCH mode, and provides the BFCH configuration unit2214 with feedback information provided from the feedback informationgenerator 2212. Otherwise, if the mode of the fast feedback channel isdetermined to the EFCH mode, the feedback mode determination unit 2210controls the feedback information generator 2212 to generate feedbackinformation including an item corresponding to the EFCH mode, andprovides the EFCH configuration unit 2216 with feedback informationprovided from the feedback information generator 2212.

In particular, the feedback mode determination unit 2210 evaluates acurrent mode of the fast feedback channel, and determines whether thecurrent mode coincides with a mode corresponding to a format of thefeedback information. If the current mode does not coincide with themode corresponding to the format of the feedback information, thefeedback mode determination unit 2210 controls the BFCH configurationunit 2214 or the EFCH configuration unit 2216 to transmit a signal for amode switching request. For example, if switching from the BFCH mode tothe EFCH mode is intended, the feedback mode determination unit 2210controls the BFCH configuration unit 2214 to configure BFCH including amode switching request code sequence for a request of switching to theEFCH mode. For example, the mode switch request code sequence is eitheran E1 code dedicatedly allocated for switching from the BFCH mode to theEFCH mode or a code sequence indicating a preferred MIMO mode using theEFCH mode to be switched. Otherwise, if switching from the EFCH mode tothe BFCH mode is intended, the feedback mode determination unit 2210controls the EFCH configuration unit 2216 to configure an EFCH includingan activated mode switch indication bit for switching to the BFCH modeor controls the BFCH configuration unit 2214 to configure a BFCHincluding a mode switch request code sequence for a request of switchingto the BFCH mode. For example, the mode switch request code sequence iseither an E2 code dedicatedly allocated for switching from the EFCH modeto the BFCH mode or a code sequence indicating a preferred MIMO modeusing the BFCH mode.

When the switching to the BFCH mode is requested, which one istransmitted between the BFCH including the mode switch request codesequence and the EFCH including the activated mode switch indication bitdiffers according to an exemplary embodiment of the present invention.That is, according to an exemplary embodiment of the present invention,either the BFCH including the mode switch request code sequence or theEFCH including the EFCH including the activate mode switch indicationbit is selectively transmitted. On the other hand, according to anotherexemplary embodiment of the present invention, the EFCH including theactivated mode switch indication bit is transmitted, and according tostill another exemplary embodiment of the present invention, the EFCHincluding the mode switch request code sequence is transmitted.

The feedback information generator 2212 generates feedback informationincluding items corresponding to the fast feedback channel's modedetermined by the feedback mode determination unit 2210. For example, ifthe mode of the fast feedback channel is the BFCH mode, the feedbackinformation generator 2212 generates feedback information indicating aCQI. Otherwise, if the mode of the fast feedback channel is the EFCHmode, the feedback information generator 2212 generates feedbackinformation indicating a CQI, a preferred sub-band, a PMI, a rank, etc.

The BFCH configuration unit 2214 configures a BFCH by using the feedbackinformation provided from the feedback mode determination unit 2210.That is, the BFCH configuration unit 2214 generates a feedback signal tobe transmitted through the fast feedback channel according to anoncoherent modulation scheme. As shown in FIG. 22B, the BFCHconfiguration unit 2214 includes a code sequence selector 2252 and achannel configuration unit 2254. The code sequence selector 2252 selectsa code sequence corresponding to the feedback information. In otherwords, the code sequence selector 2252 selects a payload correspondingto the feedback information, and then selects a code sequencecorresponding to the payload among code sequences for the BFCH. Inparticular, if the feedback mode determination unit 2210 instructs toconfigure the BFCH including a mode switching request code sequence, thecode sequence selector 2252 outputs the mode switching request codesequence. The channel configuration unit 2254 configures the BFCH byusing the code sequence. That is, the channel configuration unit 2254converts the code sequence into complex symbols, and configures the BFCHby assigning the complex symbols according to a structure of the BFCH.

The EFCH configuration unit 2216 configures an EFCH by using thefeedback information provided from the feedback mode determination unit2210. That is, the EFCH configuration unit 2216 generates a feedbacksignal to be transmitted through the fast feedback channel according toa coherent modulation scheme. As shown in FIG. 22C, the EFCHconfiguration unit 2216 includes a coder 2262, a symbol modulator 2264,and a channel configuration unit 2266. The coder 2262 codes the feedbackinformation. In this case, the coder 2262 sets a values of a modeswitching indication bit under the instruction of the feedback modedetermination unit 2210. That is, if the feedback mode determinationunit 2210 instructs to configure the EFCH including an activated modeswitching indication bit, the coder 2262 sets the mode switchingindication bit to ‘1’. Further, the coder 2262 codes the feedbackinformation bit-stream and the mode switching indication bit. The symbolmodulator 2264 modulates the coded feedback information to generatecomplex symbols, i.e., information symbols, indicating feedbackinformation to be transmitted through the EFCH. The channelconfiguration unit 2266 configures the EFCH by using the informationsymbols. That is, the channel configuration unit 2266 configures theEFCH by assigning the information symbols and the pilot symbolsaccording to a structure of the EFCH.

The subcarrier mapper 2218 maps signals to be transmitted through thefast feedback channel and provided from the BFCH configuration unit 2214or the EFCH configuration unit 2216 to resources allocated for the fastfeedback channel. The OFDM modulator 2220 converts frequency-domainsignals provided from the subcarrier mapper 2218 into time-domainsignals by performing a Fast Fourier Transform (FFT) operation, and thenconfigures OFDM symbols by inserting a CP. The RF transmitter 2222up-converts the OFDM symbols provided from the OFDM modulator 2220 intoRF signals, and then transmits the RF signals through an antenna.

A mode switching operation of a feedback channel will be described byusing the structure of the MS described in FIG. 22A above according toan exemplary embodiment of the present invention.

The feedback mode determination unit 2210 controls a feedback signalgeneration operation of the BFCH configuration unit 2214 and the EFCHconfiguration unit 2216 according to a mode of the feedback channel.

If it is determined that the mode of the feedback channel is switched tothe EFCH mode while the feedback channel operates in the BFCH mode, thefeedback mode determination unit 2210 provides control such that asignal for mode switching of the feedback channel is transmitted throughthe feedback channel, and determines switching to the EFCH mode. Forexample, the signal for mode switching is a mode switch request codesequence transmitted according to the BFCH mode. For example, the modeswitch request code sequence is either an E1 code dedicatedly allocatedfor switching from the BFCH mode to the EFCH mode or a code sequenceindicating a preferred MIMO mode using the EFCH mode to be switched.According to an exemplary embodiment in which mode switching is achievedunder the control of the BS, the feedback mode determination unit 2210determines switching to the EFCH mode upon receiving feedback channelallocation information for permitting switching to the EFCH mode.

If it is determined that the mode of the feedback channel is switched tothe BFCH mode while the feedback channel operates in the EFCH mode, thefeedback mode determination unit 2210 provides control such that asignal for mode switching of the feedback channel is transmitted throughthe feedback channel, and determines switching to the BFCH mode. Forexample, the signal for requesting the mode switching is either a modeswitch request code sequence transmitted according to the BFCH mode andfeedback information including a mode switch request transmittedaccording to the EFCH mode. For example, the mode switch request codesequence is either an E2 code dedicatedly allocated for switching fromthe EFCH mode to the BFCH mode or a code sequence indicating a preferredMIMO mode using the BFCH mode. According to another exemplary embodimentof the present invention, the feedback mode determination unit 2210determines temporary switching to the BFCH mode after transmitting thefeedback information including the mode switch request. Accordingly, thefeedback mode determination unit 2210 determines switching to the EFCHmode again when a specific duration elapses after mode switching is madeto the BFCH mode. According to still another exemplary embodiment of thepresent invention, the feedback mode determination unit 2210 providescontrol to transmit a specific code sequence within a specific duration,wherein the specific code sequence is assigned for a request ofswitching from the EFCH mode to the BFCH mode and belongs to codesequences transmissible through the fast feedback channel of the BFCHmode, and determines switching to the BFCH mode upon receiving feedbackchannel allocation information for permitting switching to the BFCHmode. Additionally, the feedback mode determination unit 2210 cancontrol the BFCH configuration unit 2214 to generate a feedback signalto be transmitted through the fast feedback channel of the BFCH modeaccording to a predefined period.

FIG. 23A is a block diagram illustrating a structure of a BS in abroadband wireless communication system according to an exemplaryembodiment of the present invention.

Referring to FIG. 23A, the BS includes an RF receiver 2302, an OFDMdemodulator 2304, a subcarrier demapper 2306, a feedback mode classifier2308, a BFCH detector 2310, an EFCH detector 2312, a feedback channelmanager 2314, and a feedback information analyzer 2316.

The RF receiver 2302 converts an RF signal received through an antennainto a base-band signal. The OFDM demodulator 2304 divides a signalprovided from the RF receiver 2302 in an OFDM symbol unit, removes a CP,and restores complex symbols mapped to a frequency domain by performingan FFT operation. The subcarrier dempper 2306 extracts a signal receivedthrough a fast feedback channel from the complex symbols mapped to thefrequency domain.

The feedback mode classifier 2308 provides a signal received through thefast feedback channel according to a mode of the fast feedback channelto the BFCH detector 2310 and the EFCH detector 2312. If a plurality offast feedback channels are respectively allocated to a plurality of MSs,the feedback mode classifier 2308 confirms the mode of the fast feedbackchannel, and provides a signal received through a fast feedback channelof each MS according to the confirmed mode to the BFCH detector 2310 orthe EFCH detector 2312. That is, the plurality of MSs may have fastfeedback channels of different modes.

The BFCH detector 2310 detects a feedback bit-stream from the signalreceived through the fast feedback channel according to the BFCH mode.That is, the BFCH detector 2310 detects the feedback bit-stream from thesignal received through the fast feedback channel according to anoncoherent demodulation scheme. In other words, the BFCH detector 2310detects a Tx code sequence by using correlation values between each ofcandidate code sequences and the received signal. Referring to FIG. 23B,the BFCH detector 2310 includes a tile divider 2352, a plurality ofcorrelation units 2354-1 to 2354-3, a plurality of squarers 2356-1 to2356-3, an adder 2358, a maximum value search unit 2360, and aninformation converter 2362. The tile divider 2352 divides a signalreceived through a fast feedback channel and provided from the feedbackmode classifier 2308 for each tile, and provides a signal for each tileto each of the correlation units 2354-1 to 2354-3. Each of thecorrelation units 2354-1 to 2354-3 performs a correlation operation onall candidate code sequences and a signal received through a tilemanaged by each correlation unit. Each of the squarers 2356-1 to 2356-3squares correlation values provided from its corresponding correlationunit 2354. The number of the correlation units 2354-1 to 2354-3 and thenumber of the squarers 2356-1 to 2356-3 are substantially identical tothe number of tiles constituting the fast feedback channel. The adder2358 adds correlation values calculated from the same candidate codesequence among square correlation values provided from the squarers2356-1 to 2356-3. That is, the adder 2358 calculates a sum of squarecorrelation values corresponding to the respective candidate codesequences. The maximum value search unit 2360 searches for a maximumunit from the sums of square correlation values to detect a Tx codesequence. The information converter 2362 evaluates a payloadcorresponding to the detected code sequence, and provides the payload tothe feedback channel manager 2314. In this case, if the detected codesequence is a mode switch request code sequence, the informationconverter 2362 informs the feedback channel manager 2314 of the factthat the mode switch request code sequence is detected. For example, themode switch request code sequence is one of an E1 code dedicatedlyassigned for switching from the BFCH mode to the EFCH mode, an E2 codededicatedly assigned for switching from the EFCH mode to the BFCH mode,a code sequence indicating a preferred MIMO mode using the EFCH mode,and a code sequence indicating a preferred MIMO mode using the BFCHmode.

The EFCH detector 2312 detects a feedback bit-stream from the signalreceived through the fast feedback channel according to the EFCH mode.That is, the EFCH detector 2312 detects the feedback bit-stream from thesignal received through the fast feedback channel according to acoherent demodulation scheme. In other words, the EFCH detector 2312detects a feedback information bit-stream by performing channelestimation, demodulation, and decoding. Referring to FIG. 23C, the EFCHdetector 2312 includes a pilot extractor 2372, a channel estimator 2374,a distortion compensator 2376, a symbol demodulator 2378, a decoder2380, and an information divider 2382. The pilot extractor 2372 extractspilot symbols from a signal received through the fast feedback channel,and then provides the pilot symbols to the channel estimator 2374 andprovides information symbols to the distortion compensator 2376. Thechannel estimator 2374 estimates a channel of the fast feedback channelby using the pilot symbols. The distortion compensator 2376 compensatesfor channel distortion of the information symbols by using the channelestimated by the channel estimator 2374. The symbol demodulator 2378demodulates the information symbols to convert them into a codebit-stream, and the decoder 2380 decodes the code bit-stream to restorea feedback bit-stream. The information divider 2382 divides the feedbackbit-stream into an information bit-stream and a mode switch indicationbit, and provides the information bit-stream to the feedback channelmanager 2314. If the mode switch indication bit is activated, theinformation divider 2382 informs the feedback channel manager 2314 ofthe fact that the activated mode switch indication bit is detected. Ifan error occurs in the feedback bit-stream, the information divider 2382informs the feedback channel manager 2314 of the error occurrence. Theerror occurrence is determined by reliability estimation on channeldecoding, a CRC processing result, etc.

The feedback channel manager 2314 provides the feedback informationanalyzer 2316 with a payload provided from the BFCH detector 2310 and aninformation bit-stream provided from the EFCH detector 2312. Further,the feedback channel manager 2314 manages a mode of a fast feedbackchannel of each MS according to the notification provided by the BFCHdetector 2310 to indicate whether the mode switch request code sequenceis detected and according to the notification provided by the EFCHdetector 2312 to indicate whether the activated mode switch indicationbit is detected. That is, if a code sequence for requesting switching tothe EFCH mode is detected by the BFCH detector 2310, the feedbackchannel manager 2314 determines to switch the fast feedback channel of acorresponding MS to the EFCH mode, and controls the feedback modeclassifier 2308 to provide a signal received through the fast feedbackchannel of the MS to the EFCH detector 2312 in a next frame.Alternatively, if the mode switch request code sequence is detected bythe BFCH detector 2310 or if the activated mode switch indication bit isdetected by the EFCH detector 2312, the feedback channel manager 2314determines to switch the fast feedback channel of the MS to the BFCHmode, and controls the feedback mode classifier 2308 to provide the BFCHdetector 2310 with the signal received through the fast feedback channelof the MS in a next frame. If the EFCH detector 2312 recognizes that anerror occurs in a feedback bit-stream, the feedback mode classifier 2308controls the feedback mode classifier 2308 to provide the BFCH detector2310 with the signal received through the fast feedback channel.

The feedback information analyzer 2316 analyzes feedback informationprovided from the feedback channel manager 2314. That is, the feedbackinformation analyzer 2316 evaluates information such as a CQI, apreferred sub-band, PMI, a rank, etc., of the MS from the feedbackinformation.

In the exemplary structure of the BS described above with reference toFIG. 23A and FIG. 23C, the BS attempts to detect the mode switch requestcode sequence for switching to the BFCH mode and also attempts to detectwhether the mode switch indication bit is activated according to anexemplary embodiment of the present invention. According to anotherexemplary embodiment of the present invention, the BS does not attemptto detect the mode switch request code sequence for switching to theBFCH mode, thereby skipping an operation for controlling the feedbackmode classifier 2308 to provide the signal received through the fastfeedback channel to the BFCH detector 2310 if an error occurs in thefeedback bit-stream. According to still another exemplary embodiment ofthe present invention, the BS does not attempt to detect whether themode switch indication bit is activated, thereby skipping an operationof the EFCH detector 2312 for determining whether the mode switchindication bit is activated.

An operation corresponding to mode switching of a feedback channel of anMS will be described according to an exemplary embodiment of the presentinvention by using the structure of the BS described above withreference to FIG. 23A.

The feedback channel manager 2314 controls operations of the BFCHdetector 2310 and the EFCH detector 2312 according to a mode of afeedback channel of an MS. That is, if the feedback channel operates inthe BFCH mode, the feedback channel manager 2314 controls the BFCHdetector 2310 to provide feedback information, and if the feedbackchannel operates in the EFCH mode, the feedback channel manager 2314controls the EFCH detector 2312 to provide feedback information.

While the feedback channel operates in the BFCH mode, if a signal forrequesting the mode switching from the BFCH mode to the EFCH mode isdetected through the fast feedback channel, the feedback channel manager2314 stops a detection operation of the BFCH detector 2310, and controlsthe EFCH detector 2312 to detect feedback information according to theEFCH mode. For example, the signal for requesting the mode switching isa mode switch request code sequence transmitted according to the EFCHmode, and the mode switch request code sequence is either an E1 codededicatedly allocated for switching from the BFCH mode to the EFCH modeor a code sequence indicating a preferred MIMO mode using the EFCH modeto be switched. According to an exemplary embodiment in which modeswitching is achieved under the control of the BS, the feedback channelmanager 2314 operates the EFCH detector 2312 after determining whetherswitching to the EFCH mode is permitted and after transmitting feedbackchannel allocation information for permitting switching to the EFCHmode. That is, although not shown, the BS includes a message generatorfor generating the feedback channel allocation information and atransmitter for transmitting the feedback channel allocationinformation, and the feedback channel manager 2314 controls the messagegenerator and the transmitter.

While the feedback channel operates in the EFCH mode, if a signal forrequesting the mode switching from the EFCH mode to the BFCH mode isdetected through the fast feedback channel, the feedback channel manager2314 stops a detection operation of the EFCH detector 2312, and controlsthe BFCH detector 2310 to detect feedback information according to theBFCH mode. For example, the signal for requesting the mode switching iseither a mode switch request code sequence transmitted according to theBFCH mode or feedback information including a mode switch requesttransmitted according to the EFCH mode. Herein, the mode switch requestcode sequence is either an E2 code dedicatedly allocated for switchingfrom the EFCH mode to the BFCH mode or a code sequence indicating apreferred MIMO mode using the BFCH mode. According to another exemplaryembodiment of the present invention, the feedback channel manager 2314temporarily allows switching to the BFCH mode. If a specific durationelapses after the BFCH detector 2310 starts to detect feedbackinformation according to the BFCH mode, the feedback channel manager2314 stops a detection operation of the BFCH detector 2310, and controlsthe EFCH detector 2312 to detect feedback information according to theEFCH mode. According to still another exemplary embodiment of thepresent invention, upon receiving a specific code sequence within aspecific duration, wherein the specific code sequence is assigned for arequest of switching from the EFCH mode to the BFCH mode and belongs tocode sequences transmissible through the fast feedback channel of theBFCH mode, the feedback channel manager 2314 controls the messagegenerator and the transmitter so that feedback channel allocationinformation for permitting switching to the BFCH mode is transmittedafter determining whether switching to the BFCH mode is permitted.Additionally, the feedback channel manager 2314 can control the BFCHdetector 2310 to detect feedback information according to the BFCH modefrom a feedback signal received through the fast feedback channel.

According to exemplary embodiments of the present invention, a mode of afast feedback channel is switched depending on a type of feedbackinformation in a broadband wireless communication system. Therefore, thefast feedback channel can be effectively operated with a limited amountof resources.

While the invention has been shown and described with reference tocertain exemplary embodiments thereof, it will be understood by thoseskilled in the art that various changes in form and details may be madetherein without departing from the spirit and scope of the invention asdefined by the appended claims and their equivalents.

What is claimed is:
 1. A method for operating a Mobile Station (MS) in awireless communication system using a fast feedback channel supportingat least two modes of the fast feedback channel, the method comprising:generating and transmitting a feedback signal through the fast feedbackchannel according to a first mode of the fast feedback channel;determining to switch a feedback mode from the first mode to a secondmode of the fast feedback channel; transmitting a signal for requestingmode switching through the fast feedback channel; receiving feedbackchannel allocation information for permitting switching to the secondmode from a Base Station (BS), the feedback channel allocationinformation comprising a feedback period and the second mode to beswitched; and generating and transmitting a feedback signal through thefast feedback channel according to the second mode indicated by thefeedback channel allocation information.
 2. The method of claim 1,wherein the first mode comprises a mode where the MS transmits a codesequence through the fast feedback channel, and wherein the second modecomprises a mode where the MS transmits at least one pilot symbol and atleast one feedback information symbol through the fast feedback channel.3. The method of claim 2, wherein the transmitting of the signal forrequesting the mode switching through the fast feedback channelcomprises transmitting a code sequence, which is assigned for a requestof the mode switching, through the fast feedback channel according tothe first mode.
 4. The method of claim 1, wherein the first modecomprises a mode where the MS transmits at least one pilot symbol and atleast one feedback information symbol through the fast feedback channel,and wherein the second mode comprises a mode where the MS transmits acode sequence through the fast feedback channel.
 5. The method of claim4, wherein the transmitting of the signal for requesting the modeswitching through the fast feedback channel comprises transmitting acode sequence, which is assigned for a request of the mode switchingthrough the fast feedback channel according to the second mode.
 6. Themethod of claim 4, further comprising transmitting feedback informationcomprising an indicator for indicating a switch to the second mode,wherein the feedback information is transmitted through the fastfeedback channel according to the first mode, and wherein the feedbackinformation is transmitted before the transmitting of the signal forrequesting the mode switching.
 7. A method for operating a Base Station(BS) in a wireless communication system using a fast feedback channelsupporting at least two modes of the fast feedback channel, the methodcomprising: detecting feedback information from a feedback signalreceived through the fast feedback channel according to a first mode ofthe fast feedback channel; receiving a signal for requesting modeswitching through the fast feedback channel; transmitting feedbackchannel allocation information for permitting the mode switching, thefeedback channel allocation information comprising a feedback period anda mode to be switched; and detecting feedback information from thefeedback signal received through the fast feedback channel according toa second mode of the fast feedback channel indicated by the feedbackchannel allocation information.
 8. The method of claim 7, wherein thefirst mode comprises a mode where a Mobile Station (MS) transmits a codesequence through the fast feedback channel, and wherein the second modecomprises a mode where the MS transmits at least one pilot symbol and atleast one feedback information symbol through the fast feedback channel.9. The method of claim 8, wherein a signal for requesting the modeswitching is a code sequence which is assigned for a request of the modeswitching and the code sequence is detected according to the first mode.10. The method of claim 7, wherein the first mode comprises a mode wherethe MS transmits at least one pilot symbol and at least one feedbackinformation symbol through the fast feedback channel, and wherein thesecond mode comprises a mode where the MS transmits a code sequencethrough the fast feedback channel.
 11. The method of claim 10, wherein asignal for requesting the mode switching is a code sequence which isassigned for a request of the mode switching and the code sequence isdetected according to the second mode.
 12. The method of claim 10,further comprising receiving feedback information comprising anindicator for indicating a switch to the second mode, wherein thefeedback information is received through the fast feedback channelaccording to the first mode, and wherein the feedback information isreceived before the receiving of the signal for requesting the modeswitching.
 13. A Mobile Station (MS) apparatus in a wirelesscommunication system using a fast feedback channel supporting at leasttwo modes of the fast feedback channel, the apparatus comprising: afirst configuration unit configured to generate a feedback signal to betransmitted through the fast feedback channel according to a first modeof the fast feedback channel; a second configuration unit configured togenerate a feedback signal to be transmitted through the fast feedbackchannel according to a second mode of the fast feedback channel; atransmitter configured to transmit the feedback signal; a determinationunit configured to control feedback signal generation operations of thefirst and second configuration units according to a feedback mode of thefast feedback channel, and, if it is determined that the fast feedbackchannel changes the feedback mode from the first mode to the secondmode, to provide control such that a signal for mode switching istransmitted through the fast feedback channel; and a receiver configuredto receive feedback channel allocation information for permittingswitching to the second mode from a Base Station (BS), the feedbackchannel allocation information comprising a feedback period and thesecond feedback mode to be switched, wherein the determination unit isfurther configured to determine to switch to the second mode indicatedby the feedback channel allocation information.
 14. The apparatus ofclaim 13, wherein the first mode comprises a mode where the MS transmitsa code sequence through the fast feedback channel, and wherein thesecond mode comprises a mode where the MS transmits at least one pilotsymbol and at least one feedback information symbol through the fastfeedback channel.
 15. The apparatus of claim 14, wherein a signal forrequesting the mode switching is a code sequence which is assigned for arequest of the mode switching and the code sequence is transmittedaccording to the first mode.
 16. The apparatus of claim 13, wherein thefirst mode comprises a mode where the MS transmits at least one pilotsymbol and at least one feedback information symbol through the fastfeedback channel, and wherein the second mode comprises a mode where theMS transmits a code sequence through the fast feedback channel.
 17. Theapparatus of claim 16, wherein a signal for requesting the modeswitching is a code sequence which is assigned for a request of the modeswitching and the code sequence is transmitted according to the firstmode.
 18. The apparatus of claim 16, wherein the transmitter transmitsfeedback information comprising an indicator for indicating a switch tothe second mode, wherein the feedback information is transmitted throughthe fast feedback channel according to the first mode, and wherein thefeedback information is transmitted before the transmitting of thesignal for requesting the mode switching.
 19. A Base Station (BS)apparatus in a wireless communication system using a fast feedbackchannel supporting at least two modes of the fast feedback channel, theapparatus comprising: a first detector configured to detect feedbackinformation from a feedback signal received through the fast feedbackchannel according to a first mode of the fast feedback channel; a seconddetector configured to detect feedback information from a feedbacksignal received through the fast feedback channel according to a secondmode of the fast feedback channel; and a manager configured to controloperations of the first and second detectors according to a feedbackmode of the feedback channel, for stopping the detection operation ofthe first detector when a signal for requesting mode switching isdetected through the fast feedback channel, to control to transmitfeedback channel allocation information for permitting the modeswitching, and to control one of the first detector and the seconddetector according to the second mode indicated by the feedback channelallocation information among the first detector and the second detectorto detect feedback information, wherein the feedback channel allocationinformation comprises a feedback period and the second mode to beswitched.
 20. The apparatus of claim 19, wherein the first modecomprises a mode where the MS transmits a code sequence through the fastfeedback channel, and wherein the second mode comprises a mode where theMS transmits at least one pilot symbol and at least one feedbackinformation symbol through the fast feedback channel.
 21. The apparatusof claim 20, wherein a signal for requesting the mode switching is acode sequence which is assigned for a request of the mode switching andthe code sequence is detected according to the first mode.
 22. Theapparatus of claim 19, wherein the first mode comprises a mode where theMS transmits at least one pilot symbol and at least one feedbackinformation symbol through the fast feedback channel, and wherein thesecond mode comprises a mode where the MS transmits a code sequencethrough the fast feedback channel.
 23. The apparatus of claim 22,wherein a signal for requesting the mode switching is a code sequencewhich is assigned for a request of the mode switching and the codesequence is detected according to the second mode.
 24. The apparatus ofclaim 22, wherein the first detector detects feedback informationcomprising an indicator for indicating a switch to the second mode,wherein the feedback information is detected according to the firstmode, and wherein the feedback information is detected before the seconddetector detects the signal for requesting the mode switching.